# Sputtered species during ion irradiation of adenine: Implications for Titan's atmospheric chemistry

Filip Matuszewski, Véronique Vuitton, Richard Rácz, Thomas Gautier, Zoltán Juhász, Béla Sulik, Duncan V. Mifsud, Sándor Biri, Gergo Lakatos, Péter Herczku, et al.

► To cite this version:

Filip Matuszewski, Véronique Vuitton, Richard Rácz, Thomas Gautier, Zoltán Juhász, et al. Sputtered species during ion irradiation of adenine: Implications for Titan's atmospheric chemistry. 2026. [hal-05527204](https://cnrs.hal.science/hal-05527204v1)

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Preprint submitted on 25 Feb 2026

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<figure><img src="image_1.png" /></figure>

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<table><tr><td>Manuscript Number:</td><td></td></tr><tr><td>Article Type:</td><td>VSI: Planetary Simulants - Research</td></tr><tr><td>Keywords:</td><td>Adenine; keV ion irradiation; Quadrupole mass spectrometry; Monte-carlo deconvolution; Titan's atmosphere; Atmospheric simulant</td></tr><tr><td>Corresponding Author:</td><td>Filip Matuszewski<br>Universite Grenoble Alpes<br>FRANCE</td></tr><tr><td>First Author:</td><td>Filip Matuszewski</td></tr><tr><td>Order of Authors:</td><td>Filip Matuszewski<br>Véronique Vuitton<br>Richárd Rácz<br>Thomas Gautier<br>Zoltán Juhász<br>Béla Sulik<br>Duncan V. Mifsud<br>Sándor Biri<br>Gergő Lakatos<br>Péter Herczku<br>K.K. Rahul<br>Sándor T.S. Kovács<br>Robert W. McCullough<br>Nigel Mason</td></tr><tr><td>Abstract:</td><td>Cassini-Huygens detected complex molecules exceeding several thousand atomic mass units in Titan's atmosphere as well as energetic O+, OH+ and H2O+ ions in Saturn's magnetosphere. The heavy molecules are suggested to be nitrogenous polycyclic aromatic hydrocarbons (PANH). The energetic ions are thought to penetrate into Titan's atmosphere, potentially modifying the structure and chemistry of these macromolecules. This study investigates the composition of chemical species sputtered into the gas-phase once energetic ions impact said macromolecules. We have irradiated thin film samples of adenine (C5H5N5), a heterocyclic aromatic, at the HUN-REN Institute for Nuclear Research (ATOMKI) in Debrecen, Hungary. The experiments varied key parameters such as ion type (Neq+, Oq+, OHq+ and H2Oq+), energies (10 and 20 keV), temperatures (150 and 300 K) and fluences (up to 2 × 1015 ions . cm-2). In-situ quadrupole mass spectrometry measured the residual gas of the experimental chamber, analysing the material that was sputtered into the gas phase during irradiation. The deconvolution of these mass spectra was done using a Monte-Carlo approach, revealing a plethora of compounds including HCN, N2, C2N2, C2H3N, C3HN, CH2N2, NH3, C2H2 and CH4. Larger species like C5H5N5, C4H4N4 and C3H3N3 were only detected at the on-set of the irradiation. The sputtering of hydrocarbons and nitriles highlights a potential feedback mechanism in Titan's atmosphere. The direct formation of CO and CO2 from PANH irradiation appears unlikely.</td></tr><tr><td>Opposed Reviewers:</td><td></td></tr></table>
Sputtered species during ion irradiation of adenine: Implications for Titan's atmospheric chemistry

Irradiation
experiment

<figure><img src="image_2.png" /></figure>

<figure><img src="image_3.png" /></figure>

**Conclusion:**
Sputtered species (HCN, N₂, CH₄, etc.) from the irradiation of adenine implicate the existence of an ion-induced feedback mechanism in Titan's atmospheric chemistry
## Highlights

# Sputtered species during ion irradiation of adenine: Implications for Titan's atmospheric chemistry

Filip Matuszewski, Véronique Vuitton, Richárd Rácz, Thomas Gautier, Zoltán Juhász, Béla Sulik, Duncan V. Mifsud, Sándor Biri, Gergő Lakatos, Péter Herczku, K.K. Rahul, Sándor T. S. Kovács, Robert W. McCullough, Nigel J. Mason

* We analyzed the chemical composition of species sputtered into the gas-phase during keV ion irradiation on adenine.

* Irradiation induces the sputtering of HCN, $N_2$, $C_2H_2$, $C_2N_2$, $CH_4$, $CH_2N_2$, $C_3HN$ and $C_2H_3N$.

* The sputtered species are key intermediates in Titan's atmospheric chemistry, supporting a ion-induced feedback mechanism.
# Sputtered species during ion irradiation of adenine: Implications for Titan's atmospheric chemistry

Filip Matuszewski<sup>a,*</sup>, Véronique Vuitton<sup>a</sup>, Richárd Rácz<sup>b</sup>, Thomas Gautier<sup>c,d</sup>, Zoltán Juhász<sup>b</sup>, Béla Sulik<sup>b</sup>, Duncan V. Mifsud<sup>b</sup>, Sándor Birj<sup>b</sup>, Gergő Lakatos<sup>b,f,g</sup>, Péter Herczku<sup>b</sup>, K.K. Rahul<sup>b</sup>, Sándor T. S. Kovács<sup>b</sup>, Robert W. McCullough<sup>h</sup> and Nigel J. Mason<sup>b,e</sup>

<sup>a</sup>Univ. Grenoble Alpes, CNRS, IPAG, Grenoble, 38000, France

<sup>b</sup>HUN-REN Institute for Nuclear Research (ATOMKI), Debrecen, H-4026, Hungary

<sup>c</sup>LATMOS-IPSL, CNRS, Sorbonne Université, UVSQ Planetary Sciences, Guyancourt, 78280, France

<sup>d</sup>LIRA, Observatoire de Paris, Université PSL, Sorbonne Université, Université Paris Cité, CNRS, CY Cergy Paris
Université, Meudon, 92195, France

<sup>e</sup>Physics and Astronomy, School of Engineering, Mathematics, and Physics, University of Kent, Canterbury, CT2 7NH, United Kingdom

<sup>f</sup>Institute of Chemistry, University of Debrecen, Debrecen, H-4032, Hungary

<sup>g</sup>Doctoral School of Chemistry, University of Debrecen, Debrecen, H-4032, Hungary

<sup>h</sup>Department of Physics and Astronomy, School of Mathematics and Physics, Queen's University Belfast, Belfast, BT7 1NN, United Kingdom

## ARTICLE INFO

Keywords:

Adenine

keV ion irradiation

Quadrupole mass spectrometry

Mass spectra deconvolution

Monte-Carlo simulation

Titan's atmosphere

Atmospheric simulant

## ABSTRACT

Cassini-Huygens detected complex molecules exceeding several thousand atomic mass units in Titan's atmosphere as well as energetic $O^+$, $OH^+$ and $H_2O^+$ ions in Saturn's magnetosphere. The heavy molecules are suggested to be nitrogenous polycyclic aromatic hydrocarbons (PANH). The energetic ions are thought to penetrate into Titan's atmosphere, potentially modifying the structure and chemistry of these macromolecules. This study investigates the composition of chemical species sputtered into the gas-phase once energetic ions impact said macromolecules. We have irradiated thin film samples of adenine ($C_5H_5N_5$), a heterocyclic aromatic, at the HUN-REN Institute for Nuclear Research (ATOMKI) in Debrecen, Hungary. The experiments varied key parameters such as ion type ($Ne^{q+}$, $O^{q+}$, $OH^{q+}$ and $H_2O^{q+}$), energies (10 and 20 keV), temperatures (150 and 300 K) and fluences (up to $2 \times 10^{15}$ ions cm$^{-2}$). In-situ quadrupole mass spectrometry measured the residual gas of the experimental chamber, analysing the material that was sputtered into the gas phase during irradiation. The deconvolution of these mass spectra was done using a Monte-Carlo approach, revealing a plethora of compounds including HCN, $N_2$, $C_2N_2$, $C_2H_3N$, $C_3HN$, $CH_2N_2$, $NH_3$, $C_2H_2$ and $CH_4$. Larger species like $C_5H_5N_5$, $C_4H_4N_4$ and $C_3H_3N_3$ were only detected at the on-set of the irradiation. The sputtering of hydrocarbons and nitriles highlights a potential feedback mechanism in Titan's atmosphere. The direct formation of CO and $CO_2$ from PANH irradiation appears unlikely.

## 1. Introduction

Over the past decades, data from various space missions and ground-based observations have revealed a complex and diverse chemical composition in the atmosphere of Saturn's moon, Titan. Besides its main constituents, molecular nitrogen ($N_2$) and methane ($CH_4$), Titan's atmosphere is filled with a plethora of minor trace components like molecular hydrogen ($H_2$), hydrogen cyanide (HCN), acetylene ($C_2H_2$), ethylene ($C_2H_4$), ethane ($C_2H_6$), propane ($C_3H_8$), cyanoacetylene (HC$_3$N), cyanogen ($C_2N_2$) (Hanel et al., 1981; Kunde et al., 1981; Samuelson et al., 1981), more complex organics like ethyl cyanide ($C_2H_5CN$) (Cordiner et al., 2015) as well as oxygen-bearing molecules like carbon dioxide ($CO_2$), carbon monoxide (CO) and water ($H_2O$) (Samuelson et al., 1983; Lutz et al., 1983; Coustenis et al., 1998), just to name a few.

Two discoveries of the Cassini-Huygens mission are especially relevant to this study. First, in Titan's atmosphere, negatively charged ions with masses up to thousands of atomic mass units were detected (Waite et al., 2007; Crary et al., 2009). These large ions, considered precursors to the lower-altitude aerosols forming Titan's haze, are best interpreted

<figure><img src="image_4.png" /></figure>

<footnote>*Corresponding author</footnote>

<footnote>matuszewskifil@gmail.com (Filip Matuszewski)</footnote>

<footnote>ORCID(s):</footnote>

<footnote>1</footnote>
as polyaromatic nitrogen-bearing hydrocarbons (PANH), although their identification remains tentative (Lavvas et al., 2013; López-Puertas et al., 2013; Haythornthwaite et al., 2021). The origin of these large ions can be traced back to the dissociation and ionization of Titan's primary atmospheric compounds, N₂ and CH₄, which consequently form species like C₂H₂, C₂H₄, C₂H₆ and HCN. Most of these reactions are the result of neutral reactions, although, ion chemistry plays a major role in the formation of larger species (<350 Da) like benzene (C₆H₆) (Vuitton et al., 2008) which has been identified through modelling efforts (Lebonnois et al., 2002; Wilson and Atreya, 2003; Lavvas et al., 2008; Delitsky and McKay, 2010) and laboratory analog experiments (Trainer et al., 2013; Sciamma-OBrien et al., 2014; Sebree et al., 2014; Yoon et al., 2014) as a major precursor to polycyclic aromatic hydrocarbons (PAH).

The second key finding involves positively charged oxygen ions in Saturn's outer magnetosphere, which likely originate from cryo-volcanic activity on Enceladus (Johnson et al., 2005; Sittler Jr et al., 2006). While O⁺ are considered the abundant ions in Titan's orbit, other ions like OH⁺ and H₂O⁺ are found as well. These ions, with energies between 1 and 100 keV, can deliver up to ~10⁶ ions·cm⁻²·s⁻¹ into Titan's atmosphere (Hartle et al., 2006a,b) with lower estimates of 0.9-4.7 × 10⁵ ions·cm⁻²·s⁻¹ (Snowden et al., 2018; Snowden and Higgins, 2021). Ions of higher energies are also present but at lower fluxes. As they enter Titan's atmosphere, they lose energy through electronic excitation and momentum transfer to surrounding molecules, primarily N₂ (Cravens et al., 2008), with deposition occurring between 1200 and 800 km in altitude. Hörst et al. (2008) demonstrated that the observed densities of CO, CO₂, and H₂O in Titan's atmosphere can be explained by the influx of O and OH or H₂O ions into Titan's upper atmosphere. Additionally, Sittler Jr et al. (2009) proposed that magnetospheric keV O-ions may either become trapped in fullerenes or contribute to the formation of CO and CO₂ upon thermalization. Furthermore, the ions may either implant or destroy the aforementioned larger and more complex organic molecules forming new potentially lighter species.

Numerous irradiation experiments to simulate space environments have been conducted on ices (Brown et al., 1984; Famá et al., 2008; Dartois et al., 2015; De Barros et al., 2022), organics (Faure et al., 2021; Quirico et al., 2023), and meteorites (Brunetto et al., 2014), reporting the sputtering of small volatiles. These sputtered species mostly consist of fragments of the irradiated material. For instance Quirico et al. (2023) found that the irradiation methanol ice leads to the sputtering of CO, CO₂, CH₄, H₂CO, H₂ and H₂O but not of CH₃OH itself.

In the ice irradiation experiments, mixtures typically composed of H₂O with organic compounds like e.g. CH₄ (Moore and Hudson, 1998; Wada et al., 2006), C₂H₆ (Khare et al., 1993; De Barros et al., 2016), C₃H₈ and C₄H₁₀ (Hand and Carlson, 2012), as well as, CH₃OH and C₆H₈ (Allamandola et al., 1988; Baratta et al., 1994; Gerakines et al., 1996; Hudson and Moore, 2000; Palumbo et al., 1999) were used to study the effects of irradiation on compounds resembling the surfaces of icy bodies. These studies have demonstrated the formation of various organic compounds, including alcohols, aldehydes and carboxylic acids. Furthermore, the irradiation of hydrogenated carbon grains, benzene (C₆H₆) and more complex aromatics like indene (C₉H₈) capped with a water ice layer produces CO₂ and CO as demonstrated by Mennella et al. (2004), Gomis and Strazzulla (2005) and Maté et al. (2024), respectively. In these particular experiments carbonaceous material was irradiated with either Heq⁺ and Arq⁺ ions or VUV photons and electrons, proving the direct irradiation-induced chemical interaction between the carbonaceous material and the water recorded via FTIR.

Apart from the FTIR, Maté et al. (2024) as well as other studies (Brown et al., 1984; Dartois et al., 2017, 2019; Faure et al., 2025) detected the decomposition products using a Quadrupole Mass Spectrometry (QMS), which has proven to be a reliable tool for the analysis of volatile species released during irradiation. The use of a QMS has been instrumental in providing sensitive, real-time detection of sputtered molecules, along with valuable information about their composition and abundance. These studies are crucial for understanding how energetic processing in space environments drives the chemical evolution of planetary surfaces, atmospheres, and interstellar materials. For instance, Faure et al. (2025) analyzed the residual gas while irradiating H₂CO ice with 74 MeV ⁸⁶Kr¹⁸⁺ ions reporting the sputtering of H₂CO as well as fragments of it like H₂, CO, C and O. While these studies provided valuable insights into the physical and chemical effects of radiation on the ice, the use of krypton ions or electrons, limits the scope of the experiment to purely radiative effects without exploring potential chemical reactions with ions themselves. Using ion beams with reactive species, such as oxygen, could reveal whether sputtered fragments react with oxygen ions to form oxygenated species.

To study the effect of ion irradiation on complex organic molecules in Titan's upper atmosphere, in this work we used adenine (C₅H₅N₅) as a simulant for the organic material that is present in Titan's atmosphere. Indeed, even if adenine has not been detected yet on Titan, it has been detected in Titan aerosol analogs, so called tholins (Pilling et al., 2009; Poch et al., 2012; Hörst et al., 2012; He and Smith, 2014; Kawai et al., 2019). It is the only nucleic base
<figure><img src="image_5.png" /><figcaption>**Figure 1:** Schematic overview of each adenine sample, layer and ion used with the corresponding energy. Samples A1, A2 and A4 were kept at 300K, while A3 was irradiated at 150K</figcaption></figure>

that lacks oxygen and as a purine, it is a heterobicyclic aromatic compound with nitrogen. Although adenine contains a higher nitrogen content (C/N = 1) than the PANHs detected in Titan's atmosphere (C/N ≥ 3, Haythornthwaite et al. (2021)), its extensive experimental characterization in previous irradiation studies makes it an ideal simulant. This amount of prior data allows us to build upon existing results rather than starting from first principles, for instance when estimating parameters such as the thin-film sample thickness. These previous studies have examined the effect of irradiating adenine with radiation sources like ions (Vignoli Muniz et al., 2017; Ada Bibang et al., 2019), UV-light (Peeters et al., 2003; Guan et al., 2010; Poch et al., 2014), X-rays (Pilling et al., 2011) and electrons (Evans et al., 2011) concentrating on the survivability of this nucleic base in space conditions. They determine the photodecomposition of their target samples by measuring the decrease in absorbance over irradiation time. Studies utilizing low-energy UV radiation consistently show that adenine exhibits greater photostability than other organic compounds such as uracil and glycine, consequently not being fully destroyed as result of the irradiation. Poch et al. (2014) were the first hinting on the formation of macromolecules increasing adenine's photostability which were later characterized using very high resolution mass spectrometry (Matuszewski et al., 2025). Studies that used higher energy sources (>150 eV) reported the destruction of adenine and fragmentation into smaller molecules (HCN, N₂ C₂H₄N₄) or radicals (CN), in solid-phase, indicated by new appearing absorption bands (Pilling et al., 2011; Vignoli Muniz et al., 2017). Vignoli Muniz et al. (2017) pointed out that the formation of N₂ is likely but difficult to confirm as such symmetric molecules are challenging to detect through FTIR. Therefore the question remains open as to what the relative abundance of each species sputtered into the gas phase is.

Analyzing the compounds that are sputtered into the gas phase during these interactions is crucial for understanding the chemical evolution of Titan's atmosphere. However, the detailed chemical interactions between these energetic ions and macromolecules remain poorly understood, highlighting the need for laboratory experiments. Such analyses can provide insight into the composition of the sputtered species, helping to bridge the gap between laboratory experiments, computational modeling and observations. In this study, we investigate the effect of irradiating adenine thin films with low energy (10 and 20 keV) Ne<sup>q+</sup>-, O<sup>q+</sup>-, OH<sup>q+</sup>-, H₂O<sup>q+</sup>-ions with in-situ infrared (IR) spectroscopy and a strong focus on in-situ quadrupole mass spectrometry (QMS) analyzing the residual gas in the experimental chamber. A deconvolution of the mass spectra using a Monte-Carlo approach will determine the relative abundance of molecules sputtered into the gas-phase when irradiating a complex organic molecule. Here, adenine will suit us as a simulant for complex organic molecules in Titan's atmosphere, providing new insights into the effects of ion irradiation on said moleculest.

## 2. Irradiation experiments

The irradiation experiments have been performed at HUN-REN Institute for Nuclear Research (ATOMKI) in Debrecen, Hungary. Here, the experimental astrochemistry chamber AQUILA (ATOMKI-Queen's University Ice Laboratory for Astrochemistry) (Rácz et al., 2024) is coupled to an electron cyclotron resonance (ECR) ion source (Biri et al., 2012, 2021). The chamber set-up permits the simultaneous production and analysis of a sample. The sample
holder carried one sample window at a time with diameter of 15 mm and a thickness of 3 mm. An oven, connected to the chamber, sublimated adenine (Aldrich ≥99%) powder at a maximum temperature of 150 °C and pressure of 6 × 10⁻⁷ mbar which then condensed onto MgF₂-windows that were either kept at 300 K or cooled down to 150 K. In total, four adenine thin-film samples, consisting of 1-4 layers, have been produced, as detailed further below. The ion source is able to generate a wide range of positive and negative singly or multiply charged atomic and molecular ions covering a kinetic energy range of 50 eV to 900 keV. For our experiments, single- and double-charged Neq⁺, Oq⁺, OHq⁺ and H₂Oq⁺ ions with energies of either 10 or 20 keV were produced. From here on, we will call these ions either "ion projectiles" or simply "projectiles" to prevent confusion with ions detected with QMS. We chose these projectiles and energies to accurately mimic the conditions found in the upper atmosphere of Titan at an altitude between 800 and 900 km (Cravens et al., 2008). During the irradiation, material is sputtered away, thus decreasing the thickness of the sample. In order to prevent the ions from penetrate one layer and implanting ions into either an underlying layer or the sample substrate, the maximum total fluence was chosen accordingly. Hence, the total fluence varied between 0.5 × 10¹⁵ and 20 × 10¹⁵ ions . cm⁻². We note that secondary effects such as electronic cascading may still extend beyond the ion stopping range and could potentially influence deeper material. However, due to the projected range being approximately < 60 nm (calculated with SRIM (Ziegler et al., 2010) for ¹⁸O ions penetrating adenine with a density of 1.5 g/cm³) and the thickness of each layer being ≥ 300 nm, such secondary effects are negligible. Figure 1 shows a schematic overview of the samples, their layers and irradiation events. Each of these irradiation events is comprised of 4 to 9 irradiation steps. For example, the first sample A1 consists of 4 adenine layers and therefore 4 irradiation events. Each event consists of 4 irradiation steps at which the sample is irradiated with set number of ions. For irradiation event #2, e.g. 2.5 × 10¹⁴ ions . cm⁻² per step which totaled in 1 × 10¹⁵ ions . cm⁻² for the whole event. A detailed listing of each irradiation event and experiment parameter can be found in Tables A.3 and A.4 in the appendix. A Fourier-transform Infrared spectrometer (FTIR, Bruker VERTEX 70v) that is installed at the chamber which allows for the acquisition of infrared (IR) spectra in between the irradiations and depositions. The detector is placed at an angle of 156.5°, puts the incident angle at 23.5°. The thickness of the individual layers was monitored by IR-spectroscopy using the Beer-Lambert law:

$$z = \frac{NM}{\rho N_a} \cos(\theta) \qquad (1)$$

where M is the molar mass of adenine (135.13 g/mol), ρ the density (1.47 g/cm³ ±1% Kilday (1978)), Na the Avogadro constant, N the column density, and θ the incident angle (23.5°). The column density N is calculated by:

$$N = \ln(10) \frac{S}{A} \qquad (2)$$

with S being the area under the 1970-3600 cm⁻¹ of the IR-spectrum also known as the α-band and the A-value of 7.9 × 10⁻¹⁶ cm molecule⁻¹ ± 4% (Saïagh et al., 2014). As the calculation of the area heavily depends on the baseline correction, a pessimistic error of 10% has been chosen for the calculation of the error on the thickness.

### 3. QMS-data analysis

The QMS for residual gas analysis (Pfeiffer QMG 250 M3, PrismaPro Compact mass spectrometer with Vacuum RGA PrismaPro 300 sensor) is detecting the molecules that are sputtered into the gas-phase as a result of the irradiation, as well as molecules that are present at any given time. Measurements have been performed continuously throughout every deposition and irradiation. The QMS is equipped with two different detectors. In Farraday-cup (FC) mode, we are able to detect species up to a mass of 300 u. The Secondary Electron Multiplier (SEM) was set up to measure compounds up to 150 u in order to speed up the number of scans. Furthermore, the SEM possesses a higher sensitivity which is advantageous for measuring very faint signals of less abundant molecules. However, because of the heightened sensitivity, it is unsuitable for measurements during the deposition of the adenine, which were done in FC-mode.

The data present intensities for masses in the range of m/z 1-150 or m/z 1-300 over time depending on the used detector. Figure 2 shows two such plots with intensities as a function of time. On the left, the intensities of mass channels m/z 18 and m/z 135 (base peaks for water and adenine, respectively) as well as the pressure in mbar are shown before and during the deposition of adenine. In the time range of 0 to 5935 seconds, an intensity and pressure drop
<figure><img src="image_6.png" /><figcaption>**Figure 2:** Intensities over relative time for the mass channels *m/z* 18 and 135 and the pressure in mbar for a deposition of adenine (left) and *m/z* 12, 18, 26, 27, 28, 42 and 52 together with the pressure in mbar for an irradiation event (right)</figcaption></figure>

can be observed which corresponds to the initial preparation of evacuating the chamber. During that time the adenine powder is starting to heat up without being deposited yet. At >5935 s, the valve of the oven is opened. At this time, the temperature has reached 80°C, which then slowly increases to >140°C where adenine is deposited onto the sample window. It is important to note that the signal intensity at the mass channel *m/z* 135 is significantly lower than that observed at *m/z* 18 and exhibits minimal variation over time. This is attributed to transmission efficiency of the QMS, where higher-mass species are generally less efficiently ionized and/or transmitted, resulting in substantially reduced signal intensities. The signal at *m/z* 135 becomes visible only after background subtraction. A more detailed discussion of this issue is provided in Section 3.1. As we suspect the adenine to be contaminated with water, the mass channel *m/z* 18 is a better indicator of sample sublimation and recondensation. The right plot shows the intensity of the mass channels *m/z* 12, 18, 26, 27, 28, 42 and 52 as well as the pressure in mbar plotted over time during an irradiation event (Figure 2, right). This particular irradiation event consists of three irradiation steps during which the intensity of the mass peaks is increasing.

**3.1. Raw data treatment**

Despite the background pressure of ~10⁻⁹ mbar, the data is underlain by signals of contaminants present in the chamber at all times (see Figure 2, signal between irradiation steps). In order to analyse and deconvolute the data, a subtraction of the background data is needed. To achieve this, the intensities of all mass channels were averaged separately over designated time ranges before and during irradiation. These time ranges were selected individually for each irradiation event to account for variations in experimental conditions. At the start and end of each irradiation event, sudden pressure changes caused by the opening and closing of the ion beam pipe valves introduced artifacts in the signal, resulting in peaks and valleys. Figure 3 shows these artifacts especially well as the signal in mass channel *m/z* 18 is one of the least intense. However, this artifact does not appear in all samples or mass channels. To prevent these signal fluctuations from skewing the averaging, the initial few seconds before and after the irradiation were excluded. Afterwards, the averaged background signal is subtracted from the averaged irradiation signal (raw data).

While it might seem clear that certain mass peaks in the spectrum are associated with definite molecules (e.g. mass peak *m/z* 18 for H₂O), each chemical species possesses a unique mass spectrum. As molecules are ionized inside the QMS, they break apart into several fragments forming a pattern displaying multiple peaks in the mass spectrum. The more complex a molecule the more complex these fragmentation patterns become. Figure 4 shows a background subtracted mass spectrum captured during the deposition of adenine together with an ideal mass spectrum of adenine from the NIST database. Both of these mass spectra do not only show a peak at *m/z* 135 (molecular mass of adenine: 135.13 g/mol) but dozens of peaks spread across the whole mass range. Furthermore, comparing both mass spectra, many, though not all, of the peaks correspond to each other. However, the intensities of these peaks appear to be inverted, with intensities generally increasing or decreasing in opposite directions as a function of *m/z*. While the main
<figure><img src="image_7.png" /><figcaption>**Figure 3:** Intensities over relative time for the mass channels *m/z* 18 showing the signal artifacts before and after each irradiation stemming from opening and closing the valve of the ion beam pipe</figcaption></figure>

peak of adenine (m/z 135) is the most intense in the NIST-mass spectrum, the same peak appears to be a minor one in the deposition mass spectrum. This is due to higher mass ions being less efficiently transmitted through the instrument. High-mass discrimination is a known phenomenon in QMS caused by fringe fields forming at the entrance of the QMS causing higher mass molecules to be inserted less efficiently (Brubaker, 1969). This issue in transmission has to be taken into account, requiring a correction of the mass spectra captured during irradiation. Major peaks of the adenine fragmentation pattern (m/z 28, 54, 81, 108 and 135) are used as reference points for whom factors are calculated by dividing the intensity of each major peak from the NIST-spectrum with the corresponding peak from the deposition spectrum. In order to calculate a correction factor for each mass channel, an exponential fit is generated. Figure 5 shows the calculated correction factor for each major peak together with the exponential fit. An individual calculation of correction factors was performed for each sample followed by a correction of each irradiation mass spectrum with its corresponding factors. Figure A.14 in the appendix shows the effect of the transmission correction on the deposition spectrum of adenine.

Even if two instruments have comparable sensitivities, their fragmentation patterns will likely differ in fragment intensities, because the relative abundances of fragments depend on the stability of the ionization products during dissociative ionization. This process is highly sensitive to the energy transfer between electrons and neutral molecules in the ion source, which in turn is dependent on the geometry of the ion source. Even micrometer-scale differences in said geometry can alter fragment spectra (McLafferty and Turecek, 1993).

## 3.2. Monte-Carlo approach

If a complex gas mixture is measured with a QMS, the fragmentation pattern of each compound are superimposed. The challenge is then to deconvolute these mass spectra of unknown chemical species mixtures. The more complex the gas mixture, the more difficult this deconvolution becomes. Conventional automated deconvolutions are done under the assumption of fixed fragmentation patterns. However, individual intensities in the fragmentation patterns change depending on the instrument's geometry, which introduces a bias. Although the differences in intensities of fragmentation patterns usually are found to be in a range of 20% to 30% (Gautier et al., 2020), in extreme cases these differences can be much higher. For example, comparing the experimental fragmentation pattern from ATOMKI with the one from the NIST database, we observe differences >100% for peaks of smaller fragments (e.g. at *m/z* 14 for N₂, relative intensities are at 5.1 % and 13.8 % for ATOMKI and NIST, respectively). Given these challenges, using a simple automated deconvolution process of our mass spectra would be impractical. For this reason, we have applied a Monte-Carlo approach to deconvolute these mass spectra in which the individual peaks of the fragmentation patterns are varied in each iteration. The applied software was developed with Matlab by Gautier et al. (2020) and has already been used to successfully analyse data from the Cassini's INMS (Serigano et al., 2020, 2022), Rosetta's COSAC mass
<figure><img src="image_8.png" /><figcaption>Figure 4: Mass spectrum obtained during the deposition of adenine in the experiment (blue) and mass spectrum from the NIST database (orange). The intensities of the main peaks in each spectrum have been normalised to 100.</figcaption></figure>

<figure><img src="image_9.png" /><figcaption>Figure 5: Correction factors for major peaks of adenine (m/z 28, 54, 81, 108 and 135) together with the exponential fit interpolating correction factors for all mass channels</figcaption></figure>

spectrometer (Leseigneur et al., 2022), as well as Huygen's GCMS (Gautier et al., 2024; Das et al., 2025). Its basic function lies in solving a system of linear equations to find the best fitting chemical composition to mass spectrometry data:

$$I_i = \sum_{j=1}^{n} F_{i,j} N_j \qquad (3)$$
<table><caption>**Table 1**
Database of compounds used in the final deconvolutions</caption><thead><tr><th>Compound name</th><th>Compound formula</th><th>Base peak [amu]</th><th>Ionization cross section [Å<sup>2</sup>]</th><th>Reference</th></tr></thead><tbody><tr><td>Diazomethane</td><td>CH<sub>2</sub>N<sub>2</sub></td><td>14</td><td>5.372</td><td>NIST</td></tr><tr><td>Methane</td><td>CH<sub>4</sub></td><td>16</td><td>4.432</td><td>NIST</td></tr><tr><td>Ammonia</td><td>NH<sub>3</sub></td><td>17</td><td>3.472</td><td>Jiménez-Escobar et al. (2018)</td></tr><tr><td>Water</td><td>H<sub>2</sub>O</td><td>18</td><td>2.642</td><td>ATOMKI</td></tr><tr><td>Neon</td><td>Ne</td><td>20</td><td>0.584</td><td>NIST</td></tr><tr><td>Acetylene</td><td>C<sub>2</sub>H<sub>2</sub></td><td>26</td><td>4.402</td><td>Plessis and Marmet (1986)</td></tr><tr><td>Hydrogen cyanide</td><td>HCN</td><td>27</td><td>3.442</td><td>NIST</td></tr><tr><td>Molecular nitrogen</td><td>N<sub>2</sub></td><td>28</td><td>2.482</td><td>ATOMKI</td></tr><tr><td>Acetonitrile</td><td>C<sub>2</sub>H<sub>3</sub>N</td><td>41</td><td>6.332</td><td>NIST</td></tr><tr><td>Carbon dioxide</td><td>CO<sub>2</sub></td><td>44</td><td>3.712</td><td>ATOMKI</td></tr><tr><td>Cyanoacetylene</td><td>C<sub>3</sub>HN</td><td>51</td><td>6.302</td><td>NIST</td></tr><tr><td>Cyanogen</td><td>C<sub>2</sub>N<sub>2</sub></td><td>52</td><td>5.342</td><td>NIST</td></tr><tr><td>1,3,5-Triazine</td><td>C<sub>3</sub>H<sub>3</sub>N<sub>3</sub></td><td>81</td><td>10.162</td><td>NIST</td></tr><tr><td>3-Amino-4-pyrazolecarbonitrile</td><td>C<sub>4</sub>H<sub>4</sub>N<sub>4</sub></td><td>108</td><td>13.522</td><td>NIST</td></tr><tr><td>Adenine</td><td>C<sub>5</sub>H<sub>5</sub>N<sub>5</sub></td><td>135</td><td>16.882</td><td>NIST</td></tr></tbody></table>

Here, the measured intensity $I_i$ for the mass channel $i$ is calculated with the fragmentation intensity $F_{i,j}$ for species $j$ and the species concentration $N_j$. This represents the conventional automated part of the process. In order to work properly, a species fragmentation pattern database is needed. The QMS used in this study ionizes molecules at 70 eV. It is important to choose fragmentation patterns that are in agreement with said instrument. Unfortunately, that is not always possible as we would have to obtain single measurements of each compound for our specific instrument. This is not only difficult in terms of time but also possibly dangerous when handling gases like e.g. hydrogen cyanide (HCN). For this reason, most of the fragmentation patterns of the compounds in our database originated from the NIST database. The fragmentation patterns of three of these compounds ($H_2O$, $N_2$ and $CO_2$) were obtained prior to the irradiation experiments by measuring pure gases with our QMS. While this dataset is considered the most reliable reference, all fragmentation patterns were treated with equal uncertainty in the Monte Carlo analysis. For the other compounds, we had to either rely on data from other studies ($C_2H_2$, Plessis and Marmet (1986); $NH_3$, Jiménez-Escobar et al. (2018)) or on the NIST database. The decision to select certain compounds from sources other than NIST arises from the uncertainty regarding the source of the data provided by NIST, making it difficult to assess its accuracy and reliability. Initial simulations were performed with a total of 41 different chemical compounds (Table A.5) whereby certain compounds were gradually taken out of the database if they did not contribute to the fit of the measured mass spectra. In the end, 15 compounds were left in our database for the final simulations. They are displayed in Table 1.

Apart from the fragmentation patterns, the database also includes the ionization cross sections of each compound which is important to determine the probability of a compound to ionize inside the QMS. We calculate the ionization cross section $\sigma$ with an adjusted regression equation from Fitch and Sauter (1983):

$$ \sigma = 0.082 + \sum_{i=1}^{4} \alpha_{i} n_{i} \qquad (4) $$
where $\alpha_i$ is the coefficient and $n_i$ the number of each atom (H, C, N, O) in the corresponding molecule. The coefficients for H, C, N and O are 0.73, 1.43, 1.20, 1.10, respectively.

The Monte-Carlo approach of the deconvolution software starts by creating a set number *n* of different randomized fragmentation databases based on our initial database, where *n* = 500 000. Here, a change is only applied to the intensities of a peak and not on the position of said peaks. Due to the above mentioned discrepancy between NIST and measured fragmentation patterns, we have set the variation *d* in our calculations to 50 %. In the next step, each database is used to decompose the measured mass spectrum individually creating a *n* number of deconvoluted mass spectra. From these 500 000 iterations, the 10% with the lowest residual values are chosen to obtain a statistical results.

Mass channels, where *m/z* < 12, show relatively high intensities which could be explained by i) the occurrence of a double charged ions (e.g. C²⁺ and N²⁺), ii) high-mass discrimination, where the signal produced by a lighter ion is higher than that of a heavier ion of similar abundance or iii) a unknown source of instrumental error. Furthermore, H₂ could be present in the gas-phase and would present its most intense peak at *m/z* 2 with possible fragmentation signals at *m/z* 1 for H⁺ and *m/z* 3 and 4 for the deuterium containing isotopologs of the hydrogen molecule.

The majority of the recorded mass spectra do not exhibit peaks above *m/z* 57. However, in spectra where such peaks are present, typically observed during the initial stages of irradiation, distinct peaks at *m/z* 135, 108, and 81 can be identified. These are attributed to C₅H₅N₅, C₄H₄N₄, and C₃H₃N₃, respectively. Incorporating these high-mass compounds into the deconvolution process presents challenges, as the software attempts to fit their low-intensity, low-mass peaks to the dominant peaks in the measured mass spectra, leading to significant overfitting. For instance, adenine (C₅H₅N₅) exhibits a minor peak at *m/z* 28, which corresponds to a major peak in the measured QMS spectra. When the software attempts to fit this minor peak to the QMS spectrum, it results in excessive overfitting of mass channels above *m/z* 57. In order to mitigate this issue, we divided the QMS spectra into two mass ranges: *m/z* 1257 and *m/z* > 57. The spectra exhibiting peaks above *m/z* 57 were fitted separately using the corresponding high-mass compounds. The contributions of these high-mass species to the intensities in the *m/z* 1257 range were then subtracted from the QMS spectra. Once this correction was applied, the deconvolution analysis was performed using the remaining compounds listed in Table 1. A similar approach was employed by Serigano et al. (2022) in the analysis of Cassini data. However, in our case, the high-mass region is significantly less complex and is predominantly influenced by a single compound.

## 4. Deconvolution results

In total, 38 QMS spectra were deconvoluted and the MS-fractions were determined for 12+3 different compounds (*m/z* 12 for *m/z* 12-57 + 3 for *m/z* > 57). Of these spectra, 8 showed mass peaks in the high mass range. Table 2 shows the fraction of the mass spectrum and the compounds attributed to these peaks. The MS-fraction for high-mass molecules is 0.20 - 5.26 %. No discernible pattern has been identified that explains the sputtering of specific high-mass molecules as a function of ion energy or projectile type. Furthermore, the observed inconsistencies in the MS-fractions remain unexplained. These variations may be attributed to limitations in the detection sensitivity, particularly in the high-mass range, which may persist despite transmission correction. The fluence at which these spectra were taken shows that the high mass peaks are only visible in the early stages of the experiment when the deposited adenine layer is still fresh. This is why, from here on, we will concentrate our deconvolution efforts on the mass range *m/z* 12-57.

Our simulated mass spectra for the mass range *m/z* 12-57 fit on average within 3.4 ± 2.1 % for the 300 K experiments and 7.4 ± 1.8 % for the 150 K experiments. A positive value indicates that the best-fit simulations slightly underestimate the intensities of the mass spectra. For example, in the 300 K experiments, 3.4 ± 2.1 % of the mass spectrum's combined intensities are not attributed to any compound or its fragments. Further explanation as to why the cold temperature experiments are more under-fitted compared to the room temperature ones will be discussed in section 4.3. Figure 6 shows an example of a deconvoluted mass spectrum of the compounds found in the gas-phase when irradiating adenine with 10 keV O⁺ ions (bottom) and the residuals expressed as Δ normalized intensity (top). The black outline bars show the measured mass spectrum while the stacked colored bars represent the median of the top 10 % of the best-fitting simulation which is normalized to the measured mass peak *m/z* 27. Each color represents one of the 12 compounds used in this simulation. In this example, the peak at *m/z* 28 shows highest Δ normalized intensity, making it the main contributor to the mass spectrum being slightly under-fit. However, due to the Δ normalized intensity being relatively small compared to the summed intensity of the whole mass spectrum, this deconvolution still fits within 1.3 %.

Each following subsection presents the dependence of the results on the free parameters considered in the experiment, which include the kind of ion projectile used, the fluence, the temperature of the target adenine, and the
<table><caption>**Table 2**
MS-fraction of larger species for the mass range *m/z* 12-135</caption><thead><tr><th>Sample</th><th>Ion</th><th>Energy<br>[keV]</th><th>Fluence<br>[×10<sup>15</sup> ions . cm<sup>-2</sup>]</th><th>Main peak<br>[m/z]</th><th>Compound</th><th>MS-fraction<br>[%]</th></tr></thead><tbody><tr><td rowspan="3">A1</td><td>Ne<sup>2+</sup></td><td>20</td><td>0.25</td><td>135</td><td>C<sub>5</sub>H<sub>5</sub>N<sub>5</sub></td><td>2.24</td></tr><tr><td>Ne<sup>2+</sup></td><td>20</td><td>0.5</td><td>81</td><td>C<sub>3</sub>H<sub>3</sub>N<sub>3</sub></td><td>0.20</td></tr><tr><td>Ne<sup>+</sup></td><td>10</td><td>0.25</td><td>135</td><td>C<sub>5</sub>H<sub>5</sub>N<sub>5</sub></td><td>5.26</td></tr><tr><td>A2</td><td>O<sup>+</sup></td><td>10</td><td>0.5</td><td>108</td><td>C<sub>4</sub>H<sub>4</sub>N<sub>4</sub></td><td>3.71</td></tr><tr><td rowspan="4">A4</td><td>OH<sup>+</sup></td><td>10</td><td>0.5</td><td>135</td><td>C<sub>5</sub>H<sub>5</sub>N<sub>5</sub></td><td>2.45</td></tr><tr><td>H<sub>2</sub>O<sup>+</sup></td><td>10</td><td>0.5</td><td>81</td><td>C<sub>3</sub>H<sub>3</sub>N<sub>3</sub></td><td>2.24</td></tr><tr><td>O<sup>+</sup></td><td>10</td><td>0.5</td><td>81</td><td>C<sub>3</sub>H<sub>3</sub>N<sub>3</sub></td><td>0.98</td></tr><tr><td>O<sup>+</sup></td><td>10</td><td>1.0</td><td>108</td><td>C<sub>4</sub>H<sub>4</sub>N<sub>4</sub></td><td>0.26</td></tr></tbody></table>

<figure><img src="image_10.png" /><figcaption>**Figure 6:** Mass spectrum in the range *m/z* 12-57 for the material sputtered into the gas-phase when irradiating an adenine thin-film with 10 keV O⁺-ions (bottom, black outline) with the median top 10 % of our best-fitting simulation (bottom, colored stacked bars) with 12 compounds. Residuals to each mass channel are shown in the top panel.</figcaption></figure>

energy of the ion beam. These results represent the MS-fraction for the mass range of *m/z* 12-57 and not quantitative mixing ratios of all gases in the chamber. Furthermore, the error bars in the following figures represent the statistical error of the *n* best-fit simulations and do not take into account the error of the intensity signals of the individual mass channels.

## 4.1. Influence of the ion projectile

Figure 7 shows the MS-fraction, defined as the relative contribution of each compound to the total signal in the mass spectrum, for all samples as a function of the 12 compounds identified in the mass spectrum. The energy, fluence and temperature for these particular MS-fractions are 10 keV, 0.5 × 10¹⁵ ions . cm⁻² and 300K, respectively.

HCN is by far the most abundant component found in the gas-phase with a MS-fraction range between 64.6 ± 5.2 % for Ne⁺ and 74.6 ± 5.6 % for O⁺. HCN is followed by N₂ with a range of 18.4 ± 0.8 % and 13.8 ± 0.8 % for the same projectiles. Compounds like C₂H₂, C₂N₂, NH₃, and H₂O can be found in the area of a single-digit in terms of percentage. The rest of the compounds are at a MS-fraction of <1 %. The results for neon in the gas-phase can be viewed as the lowest threshold for detection, where samples irradiated with O-bearing projectiles yield MS-fractions of ~0.1 % which can not be correct as there should be no neon present in the gas-phase during these specific experiments.

Samples A2 and A4 were both irradiated with O⁺, however for some compounds, MS-fractions differ significantly (e.g. N₂). Here, MS-fractions differ by ~5 % for HCN and similar behaviour can be seen for nearly all compounds.
<figure><img src="image_11.png" /><figcaption>**Figure 7:** MS-fraction for the 12 compounds in the database for irradiations with different ions (Ne⁺, O⁺, OH⁺ and H₂O⁺) at an energy of 10 keV, temperature of 300 K and fluence of 0.5 × 10¹⁵ ions cm⁻²</figcaption></figure>

The difference between both samples is the relative time of irradiation and therefore the difference in flux of the ion beam. Even though the first irradiation step of both samples reached a fluence of 0.5 × 10¹⁵ ions cm⁻², the time of the irradiation steps was ~ 71 and ~ 236 seconds for A2 and A4, respectively. This corresponds to an ion flux more than three times lower for A4 than A2 resulting in a more unstable gas density in the chamber and weaker QMS signal. Fluxes can be viewed in table A.3 and A.4 in the appendix. Because of that, A4 irradiated with O⁺ should not be taken into account when looking at the differences in MS-fraction between different projectiles.

Significant differences in MS-fractions between samples irradiated with Ne⁺ or O-bearing projectiles can be observed for the compounds C₃HN, NH₃ and CO₂. By far the largest difference between Ne⁺ and the other projectiles can be seen in the amount of NH₃ sputtered into the gas-phase. Here, MS-fractions are more than three times larger when irradiating with O-bearing projectiles. When irradiating the sample with Ne⁺, the relatively strong H₂O signal likely stems from water contamination of the adenine powder, as water could not have been produced through irradiation. As the experiments continue, the H₂O MS-fraction drops for sample A2 and A4 with the exception of A4 irradiated with H₂O⁺ where we see a relative increase compared to O⁺ (A2) and OH⁺ (A4). For other compounds detected in the gas phase, variations in MS-fractions fall within the bounds of mutual error margins, indicating no significant differences among them.

## 4.2. Effect of fluence

At varying fluence levels, we observe pronounced shifts in the relative contributions of different compounds to the mass spectral intensities, indicating substantial fluence-dependent compositional changes. Due to the averaging of intensities over the relative measurement time, the fluence represents a range for the specific irradiation step (e.g., 0.05 Ē 10¹⁵ ions cm⁻²) rather than a fixed point value. However, for simplicity, we refer to them as discrete values (e.g., 0.5 Ē 10¹⁵ ions cm⁻²) from here on. Figure 8 shows these changes for eight compounds for all mass spectra of sample A2 captured at 300 K. The compounds not shown are either not present in the gas-phase or show a high variability making it challenging to derive clear conclusions. HCN exhibits the most dramatic decrease falling from 71.3 ± 7.6% at the start of the irradiation to 39.9 ± 3.3% at 10 × 10¹⁵ ions cm⁻². As mentioned above, 39.9 ± 3.3% is the average of the data acquired while irradiating from 5 × 10¹⁵ ions cm⁻² to 10 × 10¹⁵ ions cm⁻² (see Table A.3 irradiation event #6 step 6-7). Other compounds, such as C₂N₂, also show a decrease, albeit to a lesser extent. N₂, NH₃, CH₄ and CO₂ show an increase with rising fluence. These de- and increases are in corresponding to the relative weight of each compound in the mass spectrum. Hence, the decrease of e.g. HCN could be explained by: 1) The HCN abundance in
<figure><img src="image_12.png" /><figcaption>**Figure 8:** MS fractions as a function of fluence for sample A2 at 300K for the compounds HCN, N₂ (left), NH₃, CH₄, CO₂ (middle) and C₂N₂ (right)</figcaption></figure>

<figure><img src="image_13.png" /><figcaption>**Figure 9:** MS fractions as a function of fluence for the experiment at 150 K for the compounds HCN, N₂, CH₂N₂, NH₃, C₂H₂, CH₄, H₂O</figcaption></figure>

the gas decreases, while abundances of other species increase. 2) The abundance of HCN increases but less than other species that also increase (e.g. N₂). 3) HCN decreases stronger than other species that decrease as well.

Figure 9 illustrates the results for the low-temperature sample, showing MS-fractions as a function of fluence for all gas-phase compounds detected during irradiation with O²⁺ ions at 20 keV. A similar trend to that observed at 300 K is evident: the MS-fractions for most species exhibit fluence-dependent changes. Initially, HCN dominates the mass spectrum, with 66.7 ± 4.7 % at 0.5 × 10¹⁵ ions · cm⁻², but it subsequently declines sharply to 14.0 ± 1.1 % at 2 × 10¹⁵ ions · cm⁻². N₂, with 1.7 ± 0.8 % at the start of irradiation, increases to 34.7 ± 1.3 % at a fluence of 1.25 × 10¹⁵ ions · cm⁻², followed by a decrease to 29.6 ± 1.5 % at 2 × 10¹⁵ ions · cm⁻². CH₄, NH₃, and H₂O present an increase over time as well. The compound C₂H₂ has the lowest abundance with 0.5 ± 1.7 % at the start with none being detected by the end of the experiment. All the remaining compounds from the database could not be detected.
<figure><img src="image_14.png" /><figcaption>**Figure 10:** MS-fraction for 7 compounds for different ions at an energy of 20 keV, temperature of 150 and 300 K and fluence of 0.5 × 10¹⁵ ions · cm⁻²</figcaption></figure>

## 4.3. Temperature

The deconvolution of mass spectra acquired at 150 K proved significantly more challenging compared to those taken at 300 K, because peak intensities reduced by an order of magnitude at low temperature compared to room temperature. The reason for this is that the abundance of sputtered material is influenced by temperature, as demonstrated by Davis et al. (2021). For instance, Chandra et al. (2025) reported that the sputtering yield of CO₂ from irradiated organicwater mixtures is three times lower at 80 K compared to 100 K and 120 K. As a result, certain smaller mass peaks fell below the noise threshold, making accurate analysis more challenging and leading to larger error margins. Despite this, we observe a significant difference in the MS fractions when comparing the measurements conducted at 150 K versus 300 K.

Similarly to Figure 7, Figure 10 presents the MS fractions for all measured compounds. However, instead of comparing different ion projectiles, this figure illustrates the differences between samples A2 and A3, which were both irradiated with 20 keV O²⁺ ions at 0.5 × 10¹⁵ ions · cm⁻², but at temperatures of 300 K and 150 K, respectively. Almost all compounds exhibit variations in their MS fractions when comparing the two different temperatures. The only exception is HCN, the primary component of the gas mixture, which consistently constitutes approximately 70% of the MS signal. Compounds like N₂ and C₂H₂ show higher MS fractions in the 300 K sample compared to the 150 K. The opposite is true for NH₃, H₂O and CH₄. All other compounds from Table 1, have not been found in the cold temperature experiment.

## 4.4. Energy

The samples A1 and A2 were irradiated with two different ion beam energies: 10 and 20 keV. Upon examining the impact of these varying energies on the MS fraction, it is challenging to draw definitive conclusions regarding their influence. The reason for this is, in part, due to an insufficient amount of data points. Based on the available data points, no significant changes in MS fractions are observed, likely due to the energy difference being too small.

# 5. Discussion

## 5.1. Ambiguities in the molecular interpretation of mass channel m/z 44

Interpreting mass spectra of complex chemical mixtures presents inherent challenges due to the overlapping fragmentation patterns of different molecular compounds. While certain mass channels may initially appear to correspond to specific molecules, fragmentation during ionization produces multiple peaks, leading to ambiguities
<figure><img src="image_15.png" /><figcaption>Figure 11: MS fractions of water as a function of fluence for sample A1's 1st, 2nd and 3rd adenine layer</figcaption></figure>

in molecular identification. Consequently, a given mass channel may not uniquely correspond to a single molecular species. This section discusses the difficulties associated with molecular interpretation for specific mass channels.

We tested C₃H₈, CO₂ and N₂O as potential contributors to the signal at *m/z* 44. Although these compounds have the same nominal mass, their fragmentation patterns differ significantly: CO₂ and N₂O exhibit their main peak at *m/z* 44, while C₃H₈ shows a dominant fragment at *m/z* 29. Best-fit simulations incorporating each compound were performed. Given the number of hydrogen atoms in adenine, the formation of a highly hydrogenated compound like C₃H₈ is chemically implausible under sputtering conditions. This reasoning also applies to other hydrogen-rich species with similar mass, such as C₂H₆N, for which no fragmentation pattern was available to include in our fits. Another candidate for the *m/z* 44 signal, N₂O, is chemically more consistent with nitrogen-rich fragmentation pathways. However, simulations including N₂O led to higher MS fractions in the Neq⁺ experiments compared to those with O-bearing projectiles. Simulations including only CO₂ produced similarly unexpected high MS-fractions in the Neq⁺ irradiation experiments, surpassing those observed in experiments using oxygen-bearing projectiles (see Figure 7). As neither the adenine sample nor the Neq⁺ projectiles contain oxygen, the formation of CO₂ in this set-up is surprising. The relatively high MS-fractions across all projectile types together with an oxygen-free system suggest the attribution may be incorrect. Small error bars indicate statistical confidence in the measurement, but they do not necessarily rule out missassignments in the spectral deconvolution. However, as described in the introduction, many studies have shown that water ices mixed with organic (oxygen-free) compounds leads to the sputtering of CO₂ (Mennella et al., 2004; Gomis and Strazzulla, 2005; Maté et al., 2024). From the relatively strong H₂O signal in the Ne- projectile experiment, we know that the adenine is highly contaminated with water. This suggests that we could have a similar process of CO₂ formation at hand, in which the formation of CO₂ is limited to the interaction between the sample and its contamination being excited by the energy delivered via irradiation. Hence, the sputtering of CO₂ is not a direct product of the ion projectiles bonding with atoms from the adenine. Given these ambiguities, we regard the identification of CO₂ at *m/z* 44 as the only valid candidate, however, its origin is the result of unwanted water contamination interacting with the adenine.

## 5.2. The role of gas-phase species in the formation of complex organic matter

The most significant factor impacting changes in MS-fractions is the irradiation fluence. Nearly all presented species show either an increase or decrease in MS-fractions with rising fluence. Figure 12 shows combined IR-spectra of the wavenumber range 2340-1930 cm⁻¹ at 150 K. Here, each line represents the absorbance over the chosen wavenumber range for fluences from 0 to 2 × 10¹⁵ ions · cm⁻². Normally, during the irradiation of adenine, we observe
<figure><img src="image_16.png" /><figcaption>**Figure 12:** IR-spectra for the fluences from 0 to 2 × 10¹⁵ ions · cm⁻², highlighting the growth of new bands with progressing irradiation</figcaption></figure>

a gradual decrease of absorbance over the time of irradiation as the sample is being destroyed. In Figure 12, this can be observed at 2350-2250 cm⁻¹. However, at 2250-2000 cm⁻¹ we see an increase of absorbance over time which indicates the creation of new material. Three new peaks can be observed here at 2216, 2143 and 2088 cm⁻¹ which correspond to C≡N, N=C=N and HCN, respectively. The peak at 2088 cm⁻¹ is only observed at 150 K and corresponds to HCN-ice forming on the surface of the sample (Moore and Hudson, 2003; Noble et al., 2013; Gerakines et al., 2022). In this IR-spectrum, we see a significant increase of absorbance between 0 and 0.25 × 10¹⁵ ions · cm⁻² indicating that the formation of HCN-ice is manifesting with the on-set of irradiation and slows later in the experiment.

The increase of absorbance for the nitrile band is an indicator for complex polymer-like organic molecules forming from adenine during irradiation. These novel molecules were initially proposed by Poch et al. (2014) and are likely to have two key effects on the MS fractions. Firstly, they are believed to enhance the photostability of adenine, thereby reducing the sputtering of material into the gas phase. Secondly, as new complex secondary material forms, the sputtering rate of HCN and C₂N₂ decreases, likely due to the increased photostability provided by the newly formed material. This is indicated by a decrease in MS-fractions of these species with rising fluence. These species are more readily sputtered from fresh adenine, whereas their release becomes less efficient as the irradiation progresses and the sample undergoes chemical restructuring forming complex secondary material.

Based on prior experiments in which adenine was irradiated with neon and oxygen ions, high resolution mass spectrometry analysis on the solid sample, as well as, IR-spectroscopy, indicate the formation of new complex organic molecules (NCOM)(Matuszewski et al., 2025). These experiments show that ion irradiation induces molecular restructuring, leading to the synthesis of up to 2000 NCOM per sample. All NCOM exhibit a high degree of aromaticity with aromaticity equivalent values over 2.7, classifying them as condensed aromatic structures or PANHs (Yassine et al., 2014). Furthermore, NCOM demonstrate efficient nitrogen incorporation with the N/C ratios being close, however, still smaller compared to the starting material adenine. The mechanisms underlying the formation of these molecules remain only partially understood. The presence of all the measured compounds in the gas phase indicates that they are a direct product of adenine decomposition, where its molecular structure is broken apart and reorganized into new molecular frameworks. However, some of these compounds may also remain on the surface or subsurface and contribute to the formation of NCOMs. Additionally, the loss of N₂ and other nitrogen-rich compounds explains the slightly lower N/C ratio compared to adenine in the newly formed complex organic molecules. This suggests that the irradiation process selectively removes nitrogen-rich fragments, leading to a final product with a different elemental composition than the original adenine.
## 5.3. Implications for organics in Titan's atmosphere

Nearly all compounds that were sputtered into the gas-phase during our experiments can be found in Titan's atmosphere (Hörst, 2017). The exception is CH₂N₂ which has not been detected in its atmosphere. However, for CH₂N₂, upper limits of abundance have been determined from observations (Nixon et al., 2010; Teanby et al., 2013; Khlifi et al., 1996). Among the trace compounds found in Titan's atmosphere, C₂H₄ and C₂H₆ are of relative high abundance, however we could not definitely attribute them to our mass spectra (see section 5.1), suggesting that they are not being produced via oxygen irradiation of PANHs.

Figure 13 shows a schematic overview of the chemical processes in Titan's atmosphere that lead to the formation of aerosols. Here, Figure 4 from Waite et al. (2007) is supplemented and modified to fit the process of sputtering from this study. Complex organics in the mass range of <300 Da (e.g. adenine) are irradiated with low energy ions triggering the sputtering of compounds that are similar to the ones resulting from the dissociation of N₂ and CH₄. Notably, both N₂ and CH₄ are also produced through sputtering processes during the experiment. This indicates that ion irradiation contributes to a feedback mechanism, where sputtered species can further participate in the atmospheric chemistry of Titan's atmosphere. This irradiation-induced feedback process has not been investigated before and is presented here for the first time.

Recent studies suggest that there is a discrepancy between observed and modeled mixing ratios of HCN in Titan's upper atmosphere. Current model calculations estimate HCN mixing ratios at an altitude of 900 km to be in the range of around 1‰10⁻⁴ to 6‰10⁻⁴ (Lavvas et al., 2008; Krasnopolsky, 2009; Hébrard et al., 2012; Loison et al., 2015; Vuitton et al., 2019), whereas observations indicate significantly higher values, ranging from approximately 5 × 10⁻⁴ to 3 × 10⁻³ (Vervack Jr et al., 2004; Gurwell, 2004; Shemansky et al., 2005; Kim et al., 2005; Adriani et al., 2011). These models do not yet consider the sputtering of HCN from PANHs, as our irradiation experiments demonstrated. These suggest that similar sputtering processes could take place in Titan's upper atmosphere and could serve as an additional source of HCN, among other compounds. However, considering that the difference in observational and modeling mixing ratios for HCN is ~1.5 × 10⁻³ that would amount to a density of ~7.24 × 10⁷ molecules cm⁻³ (10⁻⁴ Pa pressure and 150 K temperature at ~900 km altitude from Hörst (2017)) that are unaccounted for. Temperature and pressure are corresponding to the condition of Titan's atmosphere at ~900 km altitude (Hörst, 2017). Assuming a density of 2-3 × 10⁴ particles cm⁻³ for PANH molecules (López-Puertas et al., 2013), each individual PANH molecule would need to sputter approximately 3,000 HCN molecules in order to account for the gap between observations and modeling efforts. Given that PANH usually contain < 100 C atoms, the contribution of HCN production via ion-induced sputtering from PANHs can, at best, be considered minor. However, instead of PANH, larger and more massive negative ions may be susceptible to ion-induced sputtering and could represent another source. Coates et al. (2007) quantified the density of such negative ions with masses of < 10,000 amu to be ~200 cm⁻³. Assuming this density, each negative ion would have to sputter 362,000 HCN molecules to account for the gap, an amount that seems highly unrealistic.

Future calculations of absolute sputtering yields, based on cross-section calculations, together with the determination of precise mixing ratios of the sputtered species will be essential for quantifying the contribution of sputtering to modelling efforts.

## 6. Summary and Conclusion

In this study, we have irradiated 4 multi-layered adenine thin-film samples with Ne⁹⁺, O⁹⁺, OH⁹⁺ and H₂O⁹⁺ ions with energies of 10 or 20 keV at the HUN-REN ATOMKI facility in Debrecen, Hungary. Adenine was chosen as a simulant for complex organic molecules, namely PANHs, found in Titan's atmosphere. During the course of the experiment, QMS-measurements of the compounds which were sputtered into the gas phase have been performed. The deconvolution of the mass spectra was done using a Monte-Carlo approach, resulting in MS-fractions for 12 different chemical species. The following conclusions can be made:

1. The ion irradiation of adenine leads to the sputtering of HCN, N₂, C₂H₂, C₂N₂, CH₄, CH₂N₂, C₃HN and C₂H₃N. The sputtering of H₂O can be mostly attributed to the sputtering of water contamination of the adenine thin-film. Similarly, the origin of CO₂ in the gas-phase originates from purely irradiation-induced chemistry between adenine and water contamination.

2. The sputtered compounds like HCN, N₂, C₂H₂ and CH₄ are key intermediates in Titan's atmospheric chemistry. This suggests that sputtering not only contributes to the molecular inventory of the atmosphere but also acts as a feedback mechanism, replenishing reactive species that can further participate in the synthesis of complex organics and aerosols.
<figure><img src="image_17.png" /><figcaption>**Figure 13:** Schematic overview of the chemical processes leading to the formation of aerosols in Titan's atmosphere by Waite et al. (2007), modified to include the process of sputtering (blue) induced by energetic ions (red).</figcaption></figure>

3. With increasing fluence, the abundances of HCN and $C_2N_2$ in the gas phase decrease, indicating that their sputtering efficiency is higher in fresh adenine but decreases as irradiation-induced chemical restructuring and the formation of secondary material progress, while simultaneously, the abundances of $N_2$, $NH_3$, and $CH_4$ in the gas phase increase.

4. Larger species like $C_5H_5N_5$, $C_4H_4N_4$ and $C_3H_3N_3$ are predominantly sputtered into the gas phase during the initial stages of irradiation, when the adenine thin films remain unaltered and secondary material formation has not yet occurred.

5. The sputtering of HCN is not included in chemical models of Titan's atmosphere, which might explain the lower estimates of HCN abundance in Titan's upper atmosphere in said models. However, the amount of PANH and high-mass ions in Titan's upper atmosphere as well as the amount of sputtered HCN is not sufficient enough to explain this gap between observations and models. Therefore, the effect of material sputtered of PANHs and high-mass ions can be considered minor.

6. Oxygen-bearing compounds like CO and $CO_2$, which play an integral part in the chemistry of Titan's atmosphere, are unlikely to be the result of oxygen ion irradiation of PANH-like molecules at 10-20 keV. However, this behavior may be different for other PANHs or energies.

The accuracy of our results could be enhanced by calculating instrument-specific ionization cross sections for several compounds that are presented in this study. For instance, temperature-programmed desorption (TPD) can
be employed, wherein a solid sample is gradually heated while the desorbed species are monitored using a mass spectrometer as a function of temperature. This approach may also allow the extrapolation of ionization cross sections for hazardous compounds, such as HCN, which are otherwise challenging to handle directly (Díaz, 2024). Such calculations would allow for the determination of accurate mixing ratios which are vital for follow-up modeling efforts involving complex organic matter in Titan's atmosphere.

## 7. Acknowledgement

The authors are grateful for support from the Europlanet 2024 RI which has been funded by the European Union's Horizon 2020 Research and Innovation Program under grant agreement no. 871149. This study is also based on work from the COST Actions CA20129 MultiChem and CA22133 PLANETS, supported by COST (European Cooperation in Science and Technology). Z. Juhász is the grateful recipient of a János Bolyai Research Scholarship from the Hungarian Academy of Sciences. N. J. Mason is grateful for support received from the Research, Development, and Innovation Fund of Hungary through grant no. ADVANCED-151196. T. Gautier acknowledges funding from the Agence Nationale de la Recherche under the grant ANR-20-CE49-0004-01 for this work. A CC-BY public copyright license has been applied by the authors to the present document and will be applied to all subsequent versions up to the Author Accepted Manuscript arising from this submission, in accordance with the ANR grants' open access conditions.

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<figure><img src="image_18.png" /><figcaption>Adenine deposition spectrum - before and after transmission correction</figcaption></figure>

**Figure A.14:** Mass spectra of the adenine deposition before (blue) and after (orange) the transmission correction was applied

A. Supplementary
<caption>Table A.3</caption>

List of samples (A1 and A2) with irradiation events, steps, ions used, as well as fluences, energies, temperatures and thicknesses of the adenine thin-films; irradiation steps marked with a "*" have deconvoluted mass spectra

<table><thead><tr><th></th><th>Ion</th><th>irradiation event</th><th>Energy [keV]</th><th>Irradiation step</th><th>Fluence [× 10<sup>15</sup>ions cm<sup>-2</sup>]</th><th>Flux [10<sup>12</sup>ions cm<sup>-2</sup> s]</th><th>Temperature [K]</th><th>Thickness [nm]</th><th>QMS detector</th></tr></thead><tbody><tr><td rowspan="18">A1 (18.03.2024)</td><td rowspan="4">Ne<sup>2+</sup></td><td rowspan="4">#1</td><td rowspan="4">20</td><td>deposition</td><td></td><td></td><td rowspan="18">300</td><td>261 ± 28</td><td rowspan="4">FC</td></tr><tr><td>1</td><td>0.005</td><td>2.03</td><td>277 ± 30</td></tr><tr><td>2</td><td>0.01</td><td>1.91</td><td>274 ± 30</td></tr><tr><td>3</td><td>0.02</td><td>2.06</td><td>269 ± 29</td></tr><tr><td rowspan="2">deposition</td><td>4*</td><td>0.50</td><td>2.63</td><td>262 ± 28</td><td rowspan="2">SEM</td></tr><tr><td></td><td></td><td></td><td>190 ± 21</td></tr><tr><td rowspan="4">Ne<sup>2+</sup></td><td rowspan="4">#2</td><td rowspan="4">20</td><td>deposition</td><td></td><td></td><td>464 ± 50</td><td rowspan="4">FC</td></tr><tr><td>1*</td><td>0.25</td><td>2.49</td><td>450 ± 49</td></tr><tr><td>2*</td><td>0.50</td><td>2.39</td><td>424 ± 46</td></tr><tr><td>3*</td><td>0.75</td><td>2.35</td><td>413 ± 45</td></tr><tr><td rowspan="2">deposition</td><td>4*</td><td>1.00</td><td>2.33</td><td>402 ± 43</td><td rowspan="2">SEM</td></tr><tr><td></td><td></td><td></td><td>392 ± 42</td></tr><tr><td rowspan="4">Ne<sup>2+</sup></td><td rowspan="4">#3</td><td rowspan="4">20</td><td>deposition</td><td></td><td></td><td>605 ± 65</td><td rowspan="4">FC</td></tr><tr><td>1*</td><td>0.25</td><td>2.38</td><td>945 ± 102</td></tr><tr><td>2*</td><td>0.50</td><td>2.31</td><td>889 ± 96</td></tr><tr><td>3*</td><td>0.75</td><td>2.27</td><td>867 ± 94</td></tr><tr><td rowspan="2">deposition</td><td>4*</td><td>1.00</td><td>2.24</td><td>849 ± 92</td><td rowspan="2">SEM</td></tr><tr><td></td><td></td><td></td><td>836 ± 90</td></tr><tr><td rowspan="4">Ne<sup>+</sup></td><td rowspan="4">#4</td><td rowspan="4">10</td><td>deposition</td><td></td><td></td><td>1444 ± 156</td><td rowspan="4">FC</td></tr><tr><td>1*</td><td>0.25</td><td>2.41</td><td>1426 ± 154</td></tr><tr><td>2*</td><td>0.50</td><td>2.36</td><td>1417 ± 153</td></tr><tr><td>3*</td><td>0.75</td><td>2.32</td><td>1410 ± 152</td></tr><tr><td rowspan="4">A2 (19.03.2024)</td><td rowspan="4">O<sup>2+</sup></td><td rowspan="4">#5</td><td rowspan="4">20</td><td>deposition</td><td></td><td></td><td>576 ± 62</td><td rowspan="4">FC</td></tr><tr><td>1*</td><td>0.50</td><td>3.09</td><td>531 ± 57</td></tr><tr><td>2*</td><td>1.00</td><td>3.02</td><td>518 ± 56</td></tr><tr><td>3</td><td>1.50</td><td>3.04</td><td>506 ± 55</td></tr><tr><td rowspan="6">O<sup>+</sup></td><td rowspan="6">#6</td><td rowspan="6">10</td><td>deposition</td><td></td><td></td><td>498 ± 54</td><td rowspan="6">FC</td></tr><tr><td>4</td><td>2.00</td><td>3.01</td><td>493 ± 53</td></tr><tr><td>5*</td><td>2.50</td><td>3.05</td><td>486 ± 53</td></tr><tr><td>6*</td><td>3.00</td><td>3.04</td><td>481 ± 52</td></tr><tr><td>7*</td><td>3.50</td><td>3.04</td><td>469 ± 51</td></tr><tr><td>8*</td><td>5.00</td><td>3.00</td><td>449 ± 49</td></tr><tr><td rowspan="6">O<sup>+</sup></td><td rowspan="6">#6</td><td rowspan="6">10</td><td>deposition</td><td></td><td></td><td>493 ± 53</td><td rowspan="6">FC</td></tr><tr><td>1*</td><td>0.50</td><td>6.82</td><td>840 ± 91</td></tr><tr><td>2*</td><td>1.00</td><td>6.18</td><td>1087 ± 118</td></tr><tr><td>3*</td><td>1.50</td><td>5.91</td><td>1050 ± 114</td></tr><tr><td>4</td><td>2.00</td><td>5.84</td><td>1036 ± 112</td></tr><tr><td>5</td><td>2.50</td><td>5.72</td><td>1026 ± 111</td></tr><tr><td rowspan="4">O<sup>+</sup></td><td rowspan="4">#6</td><td rowspan="4">10</td><td>deposition</td><td></td><td></td><td>1018 ± 110</td><td rowspan="4">FC</td></tr><tr><td>6*</td><td>5.00</td><td>5.71</td><td>1009 ± 109</td></tr><tr><td>7*</td><td>10.00</td><td>5.28</td><td>980 ± 106</td></tr><tr><td>8</td><td>15.00</td><td>5.12</td><td>955 ± 103</td></tr><tr><td rowspan="2">O<sup>+</sup></td><td rowspan="2">#6</td><td rowspan="2">10</td><td>deposition</td><td></td><td></td><td>939 ± 102</td><td rowspan="2">FC</td></tr><tr><td>9</td><td>20.00</td><td>5.02</td><td>926 ± 100</td></tr></tbody></table>
<caption>Table A.4</caption>

List of samples (A3 and A4) with irradiation events, steps, ions used, as well as fluences, energies, temperatures and thicknesses of the adenine thin-films; irradiation steps marked with a "*" have deconvoluted mass spectra

<table><thead><tr><th></th><th>Ion</th><th>irradiation event</th><th>Energy [keV]</th><th>Irradiation step</th><th>Fluence [× 10<sup>15</sup>ions cm<sup>-2</sup>]</th><th>Fluence [× 10<sup>12</sup>ions cm<sup>-2</sup> s]</th><th>Temperature [K]</th><th>Thickness [nm]</th><th>QMS detector</th></tr></thead><tbody><tr><td rowspan="14">A3 (20.03.2024)</td><td rowspan="14">O<sup>2+</sup></td><td rowspan="14">#7</td><td rowspan="14">20</td><td colspan="3">deposition</td><td rowspan="14">150</td><td>170 ± 18</td><td rowspan="2">FC</td></tr><tr><td>1</td><td>0.25</td><td>2.44</td><td>312 ± 34</td></tr><tr><td>2*</td><td>0.50</td><td>2.35</td><td>296 ± 32</td><td rowspan="2">SEM</td></tr><tr><td>3</td><td>0.75</td><td>2.28</td><td>289 ± 31</td></tr><tr><td>4</td><td>1.00</td><td>2.21</td><td>283 ± 31</td><td rowspan="2">FC</td></tr><tr><td>5*</td><td>1.25</td><td>2.18</td><td>279 ± 30</td></tr><tr><td>6*</td><td>1.50</td><td>2.14</td><td>274 ± 30</td><td rowspan="3">SEM</td></tr><tr><td>7*</td><td>1.75</td><td>2.11</td><td>270 ± 29</td></tr><tr><td>8*</td><td>2.00</td><td>2.09</td><td>266 ± 29</td></tr><tr><td colspan="3">reheating 1K/min</td><td>150-300</td><td></td><td></td><td>FC</td></tr><tr><td rowspan="14">A4 (22.03.2024)</td><td rowspan="14">OH<sup>+</sup></td><td rowspan="14">#8</td><td rowspan="14">10</td><td colspan="3">deposition</td><td rowspan="14">300</td><td>424 ± 46</td><td rowspan="2">FC</td></tr><tr><td>1*</td><td>0.50</td><td>5.3</td><td>382 ± 41</td></tr><tr><td>2*</td><td>1.00</td><td>5.18</td><td>361 ± 39</td><td rowspan="2">SEM</td></tr><tr><td>3*</td><td>1.50</td><td>5.09</td><td>342 ± 37</td></tr><tr><td>4</td><td>2.00</td><td>5.04</td><td>328 ± 35</td><td rowspan="2">FC</td></tr><tr><td>5</td><td>2.50</td><td>4.94</td><td>314 ± 34</td></tr><tr><td>6</td><td>3.00</td><td>4.86</td><td>302 ± 33</td><td></td></tr><tr><td colspan="3">deposition</td><td></td><td></td><td>FC</td></tr><tr><td rowspan="6">H<sub>2</sub>O<sup>+</sup></td><td rowspan="6">#9</td><td rowspan="6">10</td><td>1*</td><td>0.50</td><td>6.88</td><td>536 ± 58</td><td rowspan="2">FC</td></tr><tr><td>2*</td><td>1.00</td><td>6.58</td><td>688 ± 74</td></tr><tr><td>3*</td><td>1.50</td><td>6.44</td><td>669 ± 72</td><td rowspan="2">SEM</td></tr><tr><td>4</td><td>2.00</td><td>6.40</td><td>661 ± 72</td></tr><tr><td>5</td><td>2.50</td><td>6.29</td><td>655 ± 71</td><td rowspan="2">FC</td></tr><tr><td>6</td><td>3.00</td><td>6.20</td><td>651 ± 70</td></tr><tr><td colspan="3">deposition</td><td></td><td></td><td>FC</td></tr><tr><td rowspan="6">O<sup>+</sup></td><td rowspan="6">#10</td><td rowspan="6">10</td><td>1*</td><td>0.50</td><td>2.09</td><td>832 ± 90</td><td rowspan="2">FC</td></tr><tr><td>2*</td><td>1.00</td><td>1.98</td><td>1022 ± 111</td></tr><tr><td>3*</td><td>1.50</td><td>1.90</td><td>983 ± 106</td><td rowspan="2">SEM</td></tr><tr><td>4</td><td>2.00</td><td>1.85</td><td>964 ± 104</td></tr><tr><td>5</td><td>2.50</td><td>1.79</td><td>947 ± 102</td><td rowspan="2">FC</td></tr><tr><td>6</td><td>3.00</td><td>1.75</td><td>934 ± 101</td></tr></tbody></table>
<caption>Table A.5</caption>

Initial database that has been reduced to 12 compounds over the course of the trial deconvolutions

<table><thead><tr><th>Nr.</th><th>Compound name</th><th>Compound formula</th><th>Ionization cross section [Å<sup>2</sup>]</th></tr></thead><tbody><tr><td>1</td><td>Hydrogen cyanide</td><td>HCN</td><td>3.442</td></tr><tr><td>2</td><td>Molecular nitrogen</td><td>N<sub>2</sub></td><td>2.482</td></tr><tr><td>3</td><td>Acetylene</td><td>C<sub>2</sub>H<sub>2</sub></td><td>4.402</td></tr><tr><td>4</td><td>Hydrogen peroxide</td><td>H<sub>2</sub>O<sub>2</sub></td><td>3.742</td></tr><tr><td>5</td><td>Water</td><td>H<sub>2</sub>O</td><td>2.642</td></tr><tr><td>6</td><td>Ammonia</td><td>NH<sub>3</sub></td><td>3.472</td></tr><tr><td>7</td><td>Methane</td><td>CH<sub>4</sub></td><td>4.432</td></tr><tr><td>8</td><td>Propane</td><td>C<sub>3</sub>H<sub>8</sub></td><td>10.212</td></tr><tr><td>9</td><td>Diazomethane</td><td>CH<sub>2</sub>N<sub>2</sub></td><td>5.372</td></tr><tr><td>10</td><td>Cyanogen</td><td>C<sub>2</sub>N<sub>2</sub></td><td>5.342</td></tr><tr><td>11</td><td>Acetonitrile</td><td>C<sub>2</sub>H<sub>3</sub>N</td><td>6.332</td></tr><tr><td>12</td><td>Neon</td><td>Ne</td><td>0.584</td></tr><tr><td>13</td><td>Cyanoacetylene</td><td>C<sub>3</sub>HN</td><td>6.302</td></tr><tr><td>14</td><td>Molecular oxygen</td><td>O<sub>2</sub></td><td>2.282</td></tr><tr><td>15</td><td>Carbon dioxide</td><td>CO<sub>2</sub></td><td>3.712</td></tr><tr><td>16</td><td>Argon</td><td>Ar</td><td>2.96</td></tr><tr><td>18</td><td>Methylamine</td><td>CH<sub>5</sub>N</td><td>6.362</td></tr><tr><td>19</td><td>Nitrous oxide</td><td>N<sub>2</sub>O</td><td>3.582</td></tr><tr><td>20</td><td>Acetamide</td><td>C<sub>2</sub>H<sub>5</sub>NO</td><td>8.892</td></tr><tr><td>21</td><td>Ethylene oxide</td><td>C<sub>2</sub>H<sub>4</sub>O</td><td>6.962</td></tr><tr><td>22</td><td>Acetone</td><td>C<sub>3</sub>H<sub>6</sub>O</td><td>9.852</td></tr><tr><td>23</td><td>Formamide</td><td>CH<sub>3</sub>NO</td><td>6.002</td></tr><tr><td>24</td><td>Formaldehyde</td><td>CH<sub>2</sub>O</td><td>4.072</td></tr><tr><td>25</td><td>Methane isocyanato</td><td>C<sub>2</sub>H<sub>3</sub>NO</td><td>7.432</td></tr><tr><td>26</td><td>Ethylene</td><td>C<sub>2</sub>H<sub>4</sub></td><td>5.862</td></tr><tr><td>27</td><td>Carbon monoxide</td><td>CO</td><td>2.612</td></tr><tr><td>28</td><td>Hydrogen azide</td><td>N<sub>3</sub>H</td><td>4.412</td></tr><tr><td>29</td><td>Popanenitrile</td><td>C<sub>3</sub>H<sub>5</sub>N</td><td>9.222</td></tr><tr><td>30</td><td>Adenine</td><td>C<sub>5</sub>H<sub>5</sub>N<sub>5</sub></td><td>16.882</td></tr><tr><td>31</td><td>Diacetylene</td><td>C<sub>4</sub>H<sub>2</sub></td><td>7.262</td></tr><tr><td>32</td><td>Formic acid</td><td>CH<sub>2</sub>O<sub>2</sub></td><td>5.172</td></tr><tr><td>33</td><td>Methanimine</td><td>CH<sub>3</sub>N</td><td>4.902</td></tr><tr><td>34</td><td>Aminoacetonitrile</td><td>C<sub>2</sub>H<sub>4</sub>N<sub>2</sub></td><td>8.262</td></tr><tr><td>35</td><td>Venylacetylene</td><td>C<sub>4</sub>H<sub>4</sub></td><td>8.722</td></tr><tr><td>36</td><td>Ethane</td><td>C<sub>2</sub>H<sub>6</sub></td><td>7.322</td></tr><tr><td>37</td><td>Allene</td><td>C<sub>3</sub>H<sub>4</sub></td><td>7.292</td></tr><tr><td>38</td><td>Propyne</td><td>C<sub>3</sub>H<sub>4</sub></td><td>7.292</td></tr><tr><td>39</td><td>3-Amino-4-pyrazolecarbonitrile</td><td>C<sub>4</sub>H<sub>4</sub>N<sub>4</sub></td><td>13.522</td></tr><tr><td>40</td><td>1,3,5-Triazine</td><td>C<sub>3</sub>H<sub>3</sub>N<sub>3</sub></td><td>10.162</td></tr><tr><td>41</td><td>1,2,4-Triazine</td><td>C<sub>3</sub>H<sub>3</sub>N<sub>3</sub></td><td>10.162</td></tr></tbody></table>
**Declaration of interests**

[x] The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

[ ] The authors declare the following financial interests/personal relationships which may be considered as potential competing interests: