Theoretical Modeling of Mass Spectrometry

Néstor F Aguirre, Sergio Díaz-Tendero, Paul-Antoine Hervieux, Manuel

Alcamí, Fernando Martín

► To cite this version:

Néstor F Aguirre, Sergio Díaz-Tendero, Paul-Antoine Hervieux, Manuel Alcamí, Fernando Martín. Theoretical Modeling of Mass Spectrometry. 29th International Conference on Photonic, Electronic, and Atomic Collisions (ICPEAC), Jul 2015, Tolède, Spain. pp.072060, 10.1088/1742-6596/635/7/072060. [hal-04780882](https://hal.science/hal-04780882v1)

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# Theoretical Modeling of Mass Spectrometry

To cite this article: Néstor F Aguirre et al 2015 *J. Phys.: Conf. Ser.* **635** 072060

View the [article online](#) for updates and enhancements.

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Theoretical Modeling of Mass Spectrometry

Néstor F. Aguirre*<fnref n="1" />, Sergio Díaz-Tendero*, Paul-Antoine Hervieux*, Manuel Alcamí*,<sup>†,‡</sup>
and Fernando Martín*,<sup>†,‡</sup>

* Departamento de Química, Módulo 13, Universidad Autónoma de Madrid, 28049, Madrid, Spain

* Institut de Physique et Chimie des Matériaux de Strasbourg, 23 rue du Loess, 67034 Strasbourg. France

† Instituto Madrileo de Estudios Avanzados en Nanociencias (IMDEA-Nanociencia), 28049 Madrid, Spain

‡ Condensed Matter Physics Center (IFIMAC), Universidad Autónoma de Madrid, 28049 Madrid, Spain.

**Synopsis** We present an implementation of the Microcanonical Metropolis Monte Carlo method based on statistical mechanics and electronic structure calculations. The method is designed to study any kind of fragmentation process. Here we show its capabilities to predict mass spectra of simple molecules.

When a highly energetic particle hits a neu-
tral molecule, part of its energy is transferred to
the molecule. If this energy exceeds the ioniza-
tion energy, ejection of one electron occurs, which
generates a molecular ion in an excited state.
Then, the molecule breaks leading to a charac-
teristic fragmentation pattern. As the excitation
energy increases, the number of channels, abun-
dance and variety of the ionized species also in-
crease. The main hypothesis of our method is
that the nature and extent of these reactions de-
pend only on the ion's structure and its internal
energy, irrespective of the ionization mechanism.

Under this hypothesis, the dynamical evolu-
tion of the many-body system is mainly guided
by the accessible phase-space. Thus, statistical
mechanics provides the appropriate theoretical
framework to conduct this kind of simulations.
In this context, we have developed the statistical
Microcanonical Metropolis Monte Carlo (M3C)
method [1, 2], which is based on a specific ran-
dom way to move in the phase-space until a
region of maximum entropy is reached, where
physical observables are computed by perform-
ing a statistical average. The minimum infor-
mation that M3C needs is the electronic energy,
molecular geometry and vibrational frequencies
for all possible molecules/fragments involved in
the fragmentation process, and the main infor-
mation provided is the breakup-curves (fragmen-
tation probabilities as a function of the excitation
energy). The mass spectrum is obtained by a
weighted sum of these curves by using the inter-
nal energy distribution of the parent ion resulting
from the process of electronic ionization.

In this contribution we will show some re-
sults for benchmark systems. In particular Fig.
1 shows the capabilities of M3C to describe the
fragmentation of the difluoromethane molecule
(CH2F2) with their associated breakup-curves.

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

<figure><img src="image_4.png" /><figcaption>**Figure 1.** Fragmentation of CH₂F₂ molecule. Upper panel, breakup-curves. Middle/lower panel, theoretical/experimental [3] mass spectrum.</figcaption></figure>

References

[1] S. Díaz-Tendero *et al* 2005 *Phys. Rev. A* **71** 033202

[2] N. F. Aguirre *et al* 2015. In preparation.

[3] P.J. Linstrom *et al* NIST Chemistry WebBook http://webbook.nist.gov (retrieved February 10, 2015)

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<footnote n="1">¹E-mail: nestor.aguirre@uam.es</footnote>