SCIENCE ADVANCES | RESEARCH ARTICLECHEMISTRY

Binding energy of solvated electrons and retrievalof true UV photoelectron spectra of liquids
Junichi Nishitani, Yo-ichi Yamamoto*, Christopher W. West, Shutaro Karashima, Toshinori Suzuki†
The electronic energy and dynamics of solvated electrons, the simplest yet elusive chemical species, is of interestin chemistry, physics, and biology. Here, we present the electron binding energy distributions of solvated electrons
in liquid water, methanol, and ethanol accurately measured using extreme ultraviolet (EUV) photoelectron spectroscopy of liquids with a single-order high harmonic. The distributions are Gaussian in all cases. Using the EUV
and UV photoelectron spectra of solvated electrons, we succeeded in retrieving sharp electron kinetic energy
distributions from the spectra broadened and energy shifted by inelastic scattering in liquids, overcoming an obstacle
in ultrafast UV photoelectron spectroscopy of liquids. The method is demonstrated for the benchmark systems of chargetransfer to solvent reaction and ultrafast internal conversion of hydrated electron from the first excited state.

A hydrated electron (​​e​−aq ​​​ ), a trapped electron in liquid water, is thesimplest reducing reagent in aqueous chemistry. This intriguing
species was identified by Hart and Boag in 1962 by pulse radiolysis
of liquid water (1). As ​​e​−aq​ ​​is generated in a living cell by radiation
impact, it has been extensively studied in radiation chemistry. e​​​ −aq​ ​​ isalso observed as a product of electron transfer reactions from photoexcited molecules in aqueous solutions. Nonetheless, the structure(2) and dynamics (3) of ​​e​−aq ​​​  are still poorly understood.
The electron binding energy (eBE) is the key quantity that determines reducing power of ​​e​−aq​ ​​. In 1990, Coe et al. (4) studied verticalelectron binding energies (VBEs; the peak energy of eBE distribution) of water cluster anions generated in molecular beams and predicted the VBE of e​​​ −aq​ ​​in bulk water to be 3.3 eV. However, it is still
debated whether an excess electron is internally bound or trappedon the surface of these clusters (5–7). If the latter, the VBE predictedusing clusters must be incorrect. Thus, it was necessary to directly
measure VBE of e​​​ −aq​ ​​in bulk water.
In 2010, four research groups independently reported the VBEof ​​e−a​ q​ ​​using photoelectron spectroscopy of liquid microjets (8–11).
All research groups reported VBEs of 3.3 to 3.7 eV, which were infair agreement with the prediction by Coe et al. (4). However, thisdid not solve the problem entirely. Yamamoto et al. (12) showed thatthese experimental estimates of VBE are possibly inaccurate because
the electron kinetic energy (eKE) is altered by inelastic scattering inliquid before emission from the liquid-gas interface. To obtain thecorrect eBE value, Luckhaus et al. (13) performed Monte Carlo simulations of electron scattering in liquid water and indicated that the
VBE is best estimated to be 3.7 eV. The calculated eBE distribution
exhibited a shoulder on the high eBE side.
The present study is aimed at accurate experimental measurement of the eBE distribution of ​​e​−aq​​​  to examine the validity of theoreticalanalysis by Luckhaus et al. (13) and also at similar measurements−​​​) in methanol and ethanol, for which
for solvated electron (​​e​solv
Monte Carlo simulation has not been performed owing to the lackof information on scattering cross sections. To this end, we used
Department of Chemistry, Graduate School of Science, Kyoto University, Kitashirakawa-­
Oiwakecho, Sakyo-Ku, Kyoto, 606-8502, Japan.
*This author contributed equally to this work.
†Corresponding author. Email: suzuki@kuchem.kyoto-u.ac.jp
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30 August 2019

ultrafast photoelectron spectroscopy with extreme ultraviolet (EUV)
probe pulses. In the EUV and soft x-ray region, the cross sections ofelastic and electron-vibron inelastic scattering decline, while electron-­electron inelastic scattering increases (14). Consequently, the primary(intact) and the secondary (scattered) eKE distributions are separated,and eBE distribution is accurately obtained from the former (15–17).
 ​​,​ we demonAfter we present the correct eBE distributions for ​​e​−solv
strate the utilization of these distributions for retrieval of sharp
spectral features from UV photoelectron spectra of solutions spectrally
blurred by inelastic scattering effects. The retrieval method substantially
improves the performance of the ultrafast UV photoelectron spectroscopy of liquids.
Our experiment is illustrated in Fig. 1A. We introduced a continuous liquid microjet of NaI solutions in water, methanol, or ethanol
into a photoionization chamber through a fused silica capillary witha 15- to 25-m inner diameter and excited the liquid microjet using−​​​. Their photoelectron spectra240- or 227-nm pulses to create e​​​ solv
were measured using 44.4-nm (27.9 eV) pulses and a 1.3-m-longmagnetic bottle time-of-flight (TOF) photoelectron spectrometer.
RESULTS AND DISCUSSION

EUV photoelectron spectroscopy of ​​e​−solv​​​
Figure 1B shows the photoelectron spectrum of an aqueous
0.5 M NaI solution measured using the 240-nm pump and 44.4-nm
probe pulses. The pump-probe delay time was 5 ps, and the spectrum was integrated for 1.8 × 108 shots. The pump pulse promoted
I− to a charge–transfer–to–solvent (CTTS) state, from which an electron
is released and thermalized in less than 5 ps (18–20). After 5 ps, e​​ −a​ q ​​​  hasonly weak interactions with a neutral I atom, and eBE exhibits nofurther change. The least squares fitting of the spectrum provides analmost perfect Gaussian centered at 3.76 ± 0.05 eV with a full
width at half maximum (FWHM) of 1.02 ± 0.04 eV (Fig. 1C). The
same Gaussian distribution centered at 3.77 ± 0.10 eV with an
FWHM of 1.02 ± 0.07 eV was also observed using different probe
photon energy of 29.45 eV (42.1 nm). The shoulder theoreticallyindicated by Luckhaus et al. (13) was not identified. Thus, the Monte
Carlo simulations were sufficiently accurate to retrieve VBE but not
as for the shape of the eBE distribution.
Similarly, Fig. 1 (D and E) respectively shows the photoelectron
spectra of e​​​ −solv​​​in methanol and ethanol. The former was measured
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INTRODUCTION

Copyright © 2019
The Authors, somerights reserved;
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for the Advancementof Science. No claim to
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Works. Distributed
under a Creative
Commons Attribution
NonCommercial
License 4.0 (CC BY-NC).

SCIENCE ADVANCES | RESEARCH ARTICLE
A

Ti:S laser
800 nm (ω),
35 fs, 1 kHz

Grating
Convex
lens

BBO

Slit

Probe
44.4 nm (18ω)

Al filter

Liquid microjet
Magnet

TM3

Tim

TM2

1.2 mJ

Kr gas

400 nm
0.4 mJ

Dichroic
mirrors

TM1(TM: toroidal mirror )

e-o

f-fl

igh

t tu

be

Delay stage
1.8 mJ

B

C

Liquid water
HOMO

1.0

Water
5 ps

0.5

1

D

2

3

4

5

6

E
Ethanol
200 psMethanol
20 ps−Fig. 1. Experimental apparatus and photoelectron spectra of ​​e​solv​​​. (A) Schematic diagram for UV pump–EUV probe photoelectron spectroscopy. OPA, optical parametricamplifier. BBO, β-BaB2O4. (B) Photoelectron spectra of an aqueous 0.5 M NaI solution at −10 and 5 ps. The eBE distributions of e​​​ −solv​​​in (C) water at 5 ps, (D) methanol at 20 ps,
and (E) ethanol at 200 ps measured in 0.5 M NaI solutions. HOMO, highest occupied molecular orbital.

Intensity (arb. units)

1.0

A

G

2.6 eV B

2.0 eV

1.4 eV D

0.9 eV

g

0.5

0.0
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4

Kinetic energy (eV)Fig. 2. Electron kinetic energy distribution Gℏ(E) created in conduction bandof ethanol by photoexcitation of ​​e​−solv​​​and photoelectron distribution gℏ(E)measured experimentally. Dashed lines are, respectively, Gℏ(E) for ℏ of (A) 5.8, (B) 5.2,−
(C) 4.6, and (D) 4.1 eV calculated using the eBE distribution of ​e​solv​ in ethanol
determined in the present study. The mean kinetic energies of Gℏ(E) are indicated.
Solid lines express gℏ(E) that are the experimental data adopted from (12).
Nishitani et al., Sci. Adv. 2019; 5 : eaaw6896

30 August 2019with the delay time of 20 ps and integration of more than 7.2 × 107 shots,
while the latter with 200 ps and 5.8 × 107 shots. The eBE distributions
are well approximated by Gaussian with the center at 3.19 ± 0.04 eV
and an FWHM of 1.16 ± 0.13 eV (Fig. 1D) and 3.21 ± 0.06 eV with an
FWHM of 1.22 ± 0.10 eV (Fig. 1E). Thermalization of ​​e−solv​ ​​​in methanol
takes longer than 20 ps, in which eBE increases by 0.14 eV as discussed
later. We measured eBE distribution for methanol at 100 ps, which
has a limited signal-to-noise ratio but further supports this conclusion(see the Supplementary Materials). Thus, VBEs of e​​​ −solv​​​ in methanol
and ethanol are best estimated to be 3.35 and 3.21 eV, respectively.
As demonstrated here, EUV photoelectron spectroscopy enables
accurate measurements of eBE distributions with minimal influence
from inelastic scattering effects, while its wide application to solution
chemistry may be limited by an extremely low signal level and experimental complexity. Ultrafast UV photoelectron spectroscopy of liquids
is much more easily implemented, while its photoelectron spectra are
influenced by inelastic scattering in the liquid. If one can correct theinelastic scattering effects, then ultrafast UV photoelectron spectroscopyof liquids will provide more detailed insights into solution chemistry.
Retrieval of eKE distribution before inelastic scattering
To overcome this obstacle in ultrafast UV photoelectron spectros ​​​measured
copy of liquids, we consider using the eBE distributions of e​​ −​solv
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approximately retrieve an eKE distribution before inelastic scatteringfrom a given PKE distribution. In the actual analysis, we expand an
experimental PKE time-energy map, IPKE(E, t), with a set of linearly
independent gi(E) and time-dependent coefficient, ci(t): ​​I​ PKE​​(E, t ) = ​∑ i​ ​​ ​c​  i​(​ t ) ​g​  i​(​ E)​, where i indicates discrete photon energies. Then, replacing gi(E) with a corresponding Gaussian-shaped eKE distribution, Gi(E), we retrieve an eKE time-energy map, IeKE(E, t), as ​​I​ eKE​
(E, t ) = ​∑ i​ ​​ ​c​  i​(​ t ) ​G​ i​(​ E)​.

in this study. The eBE distributions enable us to predict the initial
eKE distributions, Gℏ(E), created in the conduction band before
inelastic scattering, for various UV photon energies (ℏ), throughthe use of the relation eKE = ℏ − eBE. Here, we define E as theenergy measured from the vacuum level; the actual eKE in the conduction band is given by the sum of E and the electron affinity ofliquids (the energy difference between the vacuum level and the
conduction band minimum). With this definition, E is equal tophotoelectron kinetic energy (PKE) after photoemission, and we canfocus on the transformation of the distribution function before and after
electron scattering. For these photon energies, PKE distributions
after inelastic scattering, gℏ(E), have already been measured (12).
Examples are shown in Fig. 2. These Gℏ(E) − gℏ(E) pairs provide
us Gℏ(E) → gℏ(E) linear transformation under the influence of
inelastic scattering. Then, its inverse transformation enables us to

2

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100

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Retrieved
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VBE (eV)

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eKE (eV)eKE (eV)10

VBE (eV)

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PKE (eV)3

PKE (eV)

PKE (eV)A

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Ultrafast UV photoelectron spectrum of CTTS reaction
Figure 3 presents PKE maps measured for CTTS reactions from I− toethanol, methanol, and water previously reported by Okuyama et al.
(18) along with the retrieved eKE maps and time evolution of VBE
value (see the Supplementary Materials for details). The original PKE
maps measured for ethanol and methanol are spectrally rather

3.0

2.5

−1 0

1

2

3 10

Delay (ps)

100

3.0

2.5

−1 0

Delay (ps)Fig. 3. Ultrafast UV photoelectron spectra of CTTS reaction from I− to polar protic solvents. PKE time-energy map measured for (A) ethanol, (B) methanol, and(C) water using 226-nm pump and 260-nm probe pulses. (D to F) The eKE time-energy map retrieved from (A) to (C), respectively. (G to I) Time evolution of VBE obtained
from (A) to (C) (black) and (D) to (F) (red), respectively. The time axes are in linear scale from −1 to 3 ps and in log scale from 3 to 500 ps. Broken lines indicate the boundaryof the two scales.
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broad. On the other hand, the retrieved spectrum exhibits a narrower
spectral width and an upshifted kinetic energy distribution in allcases, as inelastic scattering effects were corrected. Figure 3 (G to I)
respectively shows the time evolution of VBE obtained from theoriginal and retrieved spectra of CTTS reaction from I− to ethanol,
methanol, and water. The amount of time-dependent energy shift
appears significantly larger for retrieved data than that for originalones, reflecting an inelastic scattering effect. The difference diminishes
in the order of ethanol, methanol, and water because VBE increases
in this order and eKE diminishes for a given probe photon energy;
the inelastic scattering effect diminishes for smaller eKE in thisenergy region. The ultrafast spectral shift in the CTTS reaction is−​  ​​, which isdue to solvation dynamics in the ground state of ​esolv
expressed using the following time-correlation function
VBE(t ) − VBE(∞)
  
  ​​	
	​
C(t ) = ​───────────
VBE(0 ) − VBE(∞)(1)

Ultrafast UV photoelectron spectrumof internal conversion of ​​e​−aq​​​
Internal conversion from the excited state of ​​e​−aq​​​  has been investigatedextensively by a number of experimentalists and theorists; however,its dynamics are still in intense debate (3, 21–26). The lifetime in the
excited state of e​​ −a​ q​​​  has been estimated with UV photoelectron spectroscopy in some reports (3, 27), while the solvation dynamics in the
ground state after the internal conversion has not been examined indetail. In the present study, we performed ultrafast photoelectron
1.0

A

1.0

B

1.0

C
Original
Retrieved

1.0 and 42 ps
0.5

1.1 and 45 ps

0.6 and 15 ps
0.5

0.8 and 20 ps

0.0

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20

Delay (ps)40

0.4 and 1.3 ps
0.5

0.4 and 2.7 ps

CONCLUSION

0.0
0

20

40

Delay (ps)020

Delay (ps)40

Fig. 4. Time-correlation function C(t) determined from ultrafast UV photoelectron
spectra of CTTS reaction from I− to polar protic solvents. (A) ethanol, (B) methanol,and (C) water. The original (black) and retrieved (red) data points are shown. Time
constants and simulated curves in solid line were obtained by the least squares
fitting. In (C), an unexpected increase of C(t) by less than 0.1 is seen after 25 ps,
which was excluded from the least squares fitting.
Nishitani et al., Sci. Adv. 2019; 5 : eaaw6896

30 August 2019−
We have measured accurate eBE distributions of ​esolv​  ​​ in threepolar protic solvents by EUV photoelectron spectroscopy andfound them to be Gaussian. These distributions were used to retrieve
true eBE distributions from UV photoelectron spectra. Our results
demonstrate that the retrieval method greatly assists extraction of clear
dynamical features from ultrafast UV photoelectron spectra, whichwere previously blurred and energy shifted by inelastic scattering effects.

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Figure 3 (G to I) provides C(t) as shown in Fig. 4[(A) ethanol, (B)methanol, and (C) water], respectively. All correlation functions
exhibit biexponential decay. The shorter time constants are subpicoseconds to picoseconds, and the longer ones are several tens ofpicoseconds in alcohols, while subpicosecond and picosecond time
constants are found in water. The time constants for original andretrieved data are similar. Comparison of the three solvents illustrates
the ultrafast solvation of ​​e​−aq ​​;​  solvation dynamics of electrons in methanol and ethanol take a considerably longer time than in water, although
all these CTTS dynamics occur in the presence of solvation shell for
I−. Thus, the extraction of the correlation functions with solvation
time constants provides us deeper insights into the solvation dynamics
of an excess electron, while recombination between an excess electron and an iodine atom has already been discussed with a global fit
analysis of the spectra or a diffusion equation (18–20).

spectroscopy of e​​​ a−q​  ​​with the 720-nm pump pulses and 270-nm
probe pulses and applied the retrieval method described above. The​​e−a​ q ​​​  were created by CTTS from Br − using 200-nm pulses andthermalized for 500 ps, which was more than sufficient as we havealready seen in Fig. 3I. Figure 5A is the eBE time-energy map directly
converted from experimental PKE distributions, while Fig. 5B is asimilar map using the retrieval method (see the Supplementary
Materials for details). The red color corresponds to the pump-probe
enhance signal, while the blue color is of the ground-state bleach(depopulation). Both appear with the cross-correlation time of thelaser pulses. The enhanced signal appearing in the eBE region of
2 to 3 eV is of the excited electronic state, and it decays very rapidly
within ca. 60 fs, while the bleach recovery occurs with a considerably longer time constant. This is because internal conversion createsa nonequilibrium state in the ground state, which undergoes solvation
dynamics to reach the thermal equilibrium. For detailed analysis of
the experimental data, we have calculated the ground-state bleachsignal (Fig. 5C) using the photoelectron spectrum separately measured and retrieved for ​​e​−aq​ ​​at thermal equilibrium and subtracted itfrom the retrieved pump-probe photoelectron spectra (Fig. 5B) toobtain the genuine pump-probe enhance signal with the positive sign
(Fig. 5D). The time-energy map thus consists of photoemission fromthe excited and ground electronic states at nonequilibrium, both ofwhich exhibit ultrafast spectral shift owing to solvation dynamics.
We separated the map into the contributions from the ground(Fig. 5E) and excited (Fig. 5F) states using their difference ineBE. The latter exhibits ultrafast decay in 64 fs, supporting previous
experimental reports (3, 27) and the nonadiabatic model of the dynamics; theoretical calculations predicting the internal conversion
lifetime to be on the order of 300 fs likely involve some inaccurate
assumptions or approximations (21). One can see that the apparent
photoemission intensity increases with internal conversion in
Fig. 5D; however, note that the photoemission intensity from theexcited state is underestimated owing to its lifetime, which is shorter
than the cross-correlation time of the laser pulses. We have deconvoluted the cross-correlation time from the measured time-­
energy map, as shown in Fig. 5G, which reveals a greater photoemission
cross section for the excited state than the ground state. Thus, weconclude that the photoemission cross section diminishes upon internal conversion. We are preparing an ultrafast laser system with a higher
time resolution to experimentally confirm this conclusion and further
elucidate the detail of this fundamental system. From Fig. 5E, C(t)in the ground state is extracted as shown in Fig. 6. The correlation function exhibited biexponential decay with the time constants of 230
and 910 fs. These time constants are in reasonable agreement with thesolvation time constants reported for liquid water (28–31). Liquid water
should have an ultrafast inertial response within about 10 fs; however,it cannot be observed in the present case, as the ground state is
created with a finite nonadiabatic reaction time from the excited state.

SCIENCE ADVANCES | RESEARCH ARTICLE

AeBE (eV)eBE (eV)

4
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E
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600

Delay (fs)Fig. 5. Ultrafast UV photoelectron spectra of internal conversion of ​​e​−aq​.​​ (A) eBE time-energy map measured for ultrafast internal conversion of ​​e​−aq​​​with the 720-nm
pump and 270-nm probe pulses. (B) Retrieved eBE time-energy map. (C) Negative signals component calculated from the photoelectron spectrum separately measured
and retrieved for e​​ −a​ q​​​at thermal equilibrium. (D) Positive signal component of the distribution calculated from (B) and (C). (E) Signal from the ground state in (D). (F) Signal
from the excited state in (D). (G) Prediction of photoelectron spectra obtained with 5-fs time resolution.

MATERIALS AND METHODS

1.0

0.5

230 and 910 fs

0.0

0

1000

2000

3000

4000

5000

Delay (fs)Fig. 6. Time-correlation function C(t) in the ground state of e​​​ −aq​​​calculated from thedata shown in Fig. 5E. Time constants and simulated curves in solid line wereobtained by the least squares fitting.
Nishitani et al., Sci. Adv. 2019; 5 : eaaw6896

30 August 2019

Ultrafast EUV photoelectron spectroscopy
The schematic diagram of our experimental setup is illustrated in
fig. S1A. We introduced a continuous liquid microjet into a photoionization chamber through a 25-m- and 15-m-inner-diameter
capillary for water and alcohols, respectively. Flow rates were 0.5,
0.25, and 0.15 ml/min for water, methanol, and ethanol, respectively.
A Ti:sapphire regenerative amplifier [800 nm (), 1 kHz, 35 fs] wasused to generate UV pump and EUV probe pulses (32). The UV
pulses were generated using an optical parametric amplifier andfocused on a liquid microjet using an Al concave mirror (r = 2000 mm).
Pump wavelengths were 240 and 227 nm for water and alcohols,
respectively. The maximum UV pulse energies at the sample were
250, 200, and 130 nJ for water, methanol, and ethanol, respectively.
The EUV pulses were generated in a Kr gas using 2 (400 nm, <400 J)
as a driving laser, and the single-order 18 (44.4 nm, 27.9 eV) radiation was selected using a home-made time-preserving monochromator based on the design by Frassetto et al. (33). The EUV pulses
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were focused on the sample with a toroidal mirror. The photon fluxof 18 was <1 × 109 photons/s; the radiation of the neighboring orders,14 and 22, was undetected. The experiment was also performed
with 19 (42.1 nm, 29.45 eV) radiation produced by an 800-nm
driving laser for comparison. The PKE distribution was measured
using a 1.3-m-long magnetic bottle TOF photoelectron spectrometer.
A magnetic bottle collected more than 50% of the electrons emitted
from the liquid microjet. The energy resolution of the spectrometer
was 50 meV. We accelerated photoelectrons from liquid by applying −15 V to the liquid-discharging nozzle and applied a retardation
voltage of −27 V to the TOF analyzer to reject electrons with PKE lessthan 12 eV, which enabled us to remove the gaseous photoelectron bands
from the spectral region of interest. The measured PKE was energy-­
calibrated using a photoelectron band of the highest occupied molecularorbital of each solvent; we used 11.3 (34), 9.96, and 9.54 eV measured
in our laboratory for water, methanol, and ethanol, respectively.

Ultrafast UV photoelectron spectroscopy
The experimental data on CTTS reaction from I− to polar protic
solvents were published by Okuyama et al. (18). The internal conversion of e​​​ −aq​ ​​was newly measured in the present work. A 15-m-­diameter liquid microjet was injected into the vacuum and illuminated at
1 mm downstream from the nozzle with three laser pulses for synthesis,
pump, and probe of e​​​ a−q ​​​  . The driving laser was a 10-kHz one box
Ti:sapphire laser with 35-fs pulse duration. The synthesis pulses(200 nm) excited Br− in a 0.3 M NaBr aqueous solution to create​​ REFERENCES AND NOTES​​ −aq ​​​  thus created were thermalized fore​−aq ​​​  by the CTTS reaction. The e​
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water [11.3 eV; (34)] is far greater than the probe photon energy, noof the hydrated electron. Science 342, 1496–1499 (2013).
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axis perpendicular to the liquid jet and laser beams. All of the laser
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9.

SUPPLEMENTARY MATERIALSSupplementary material for this article is available at http://advances.sciencemag.org/cgi/
content/full/5/8/eaaw6896/DC1
Supplementary Text
Section S1. EUV photoelectron spectrometer and eBE distribution of e​​​ −solv​​​in methanol at thedelay time of 100 ps
Section S2. Retrieval of eKE distribution before inelastic scattering
Section S2.1. Energy-dependent transmission efficiency T(E) at liquid-gas interface
Section S2.2. Influence of T(E) on estimated yield of ​​e​−solv​​​
Section S3. Retrieval method
Section S3.1. Basis functions
Section S3.2. Determination of expansion coefficients
Section S3.3. Transformation of gi(E) to Gi(E)
Section S3.4. Compatibility of the basis functions among three solvents
Section S3.5. Influence of the number of basis functions on spectral retrieval
Section S4. Results of least squares fitting determining the expansion coefficients
Section S4.1. CTTS reaction from I− to ethanol, methanol, and water
Section S4.2. Internal conversion of ​​e​−aq​​​
Section S5. Comparison of kinetic time constants of original and retrieved spectra

Nishitani et al., Sci. Adv. 2019; 5 : eaaw6896

30 August 2019

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Section S5.1. Global fitting results of the spectra measured for CTTS reaction from I− toethanol, methanol, and water
Section S6. Deconvolution of cross-correlation function from the observed time-energy map
Fig. S1. Ultrafast EUV photoelectron spectroscopy of liquids.
Fig. S2. Influence of T(E) on color map and yield.
Fig. S3. An example of retrieving process.
Fig. S4. Influence of T(E) on retrieving results.
Fig. S5. Comparisons of PKE spectra resulting from same eKE distribution among three solvents.
Fig. S6. Dependence of spectral retrieval on the number of basis functions.
Fig. S7. Fitting of photoemission signal obtained for NaI ethanol solution as a function of delay
time between pump (226 nm) and probe (260 nm) pulses.
Fig. S8. Fitting of photoemission signal obtained for NaI methanol solution as a function ofdelay time between pump (226 nm) and probe (260 nm) pulses.
Fig. S9. Fitting of photoemission signal obtained for aqueous NaI solution as a function ofdelay time between pump (226 nm) and probe (260 nm) pulses.
Fig. S10. Fitting of photoemission signal obtained for internal conversion of e​​​ −aq​​​at 84 fs.
Fig. S11. Fitting of photoemission signal obtained for internal conversion of e​​​ −aq​​​as a function ofdelay time between pump (720 nm) and probe (270 nm) pulses.
Fig. S12. Global fit of the original and retrieved spectra of CTTS reaction from I− to ethanol.
Fig. S13. Global fit of the original and retrieved spectra of CTTS reaction from I− to methanol.
Fig. S14. Global fit of the original and retrieved spectra of CTTS reaction from I− to water.
Table S1. Basis function used in the retrieval of the spectra of CTTS reactions from I− in threesolvents.
Table S2. Basis function used in the retrieval of the spectra of internal conversion of e​​​ −aq​.​​
Table S3. Number of basis functions used for simulation shown in fig. S6 and their energy
spacings.
Table S4. Fitting parameters obtained by global fitting of the spectra of CTTS reactions fromI− in three solvents.
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Submitted 16 January 2019
Accepted 24 July 2019
Published 30 August 201910.1126/sciadv.aaw6896
Citation: J. Nishitani, Y.-i. Yamamoto, C. W. West, S. Karashima, T. Suzuki, Binding energy ofsolvated electrons and retrieval of true UV photoelectron spectra of liquids. Sci. Adv. 5,
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Binding energy of solvated electrons and retrieval of true UV photoelectron spectra of liquids
Junichi Nishitani, Yo-ichi Yamamoto, Christopher W. West, Shutaro Karashima and Toshinori Suzuki

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DOI: 10.1126/sciadv.aaw6896

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