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Home All issues Volume 710 (June 2026) A&A, 710 (2026) A94 Full HTML
Open Access
Issue
A&A
Volume 710, June 2026
Article Number A94
Number of page(s) 6
Section Astrophysical processes
DOI https://doi.org/10.1051/0004-6361/202659133
Published online 03 June 2026

© The Authors 2026

Licence Creative CommonsOpen Access article, published by EDP Sciences, under the terms of the Creative Commons Attribution License (https://creativecommons.org/licenses/by/4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

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1. Introduction

Aromatics permeate every corner of our Universe (Kaiser & Hansen 2021). For decades, the presence of polycyclic aromatic hydrocarbons (PAHs), representing 10–20% of the interstellar carbon, was inferred indirectly (Hrodmarsson et al. 2025); they collectively caused the widespread aromatic infrared bands (AIBs), which dominate the emission spectra of rich-dust astrophysical environments (Leger & Puget 1984; Allamandola et al. 1989). Infrared observations suggested PAHs pervade the interstellar medium (ISM) – as they are particularly abundant in environments associated with star formation – such as photodissociation regions (PDRs), planetary nebulae, and protoplanetary disks. This ubiquity is supported by their detection in primitive extraterrestrial matter, including samples from the Ryugu asteroid (Hayabusa2 probe) (Sabbah et al. 2024) and primitive carbonaceous chondrites such as Murchison (Sephton 2005). Smaller PAH family members have also been detected in comets, such as 81P/Wild 2 (Sandford et al. 2006) and 67P/Churyumov–Gerasimenko (Hänni et al. 2022).

A major breakthrough was the recent radio-detection of specific PAHs – many being derivatives – in the cold, dense Taurus molecular cloud (TMC-1) (see, e.g., Cernicharo et al. 2021; Burkhardt et al. 2021; Cabezas et al. 2025; Wenzel et al. 2024). These discoveries confirm that complex aromatic synthesis is active even in the earliest stages of star and planet formation. Benzene (C6H6), the principal building block of PAHs (Langer et al. 2023; Lemmens et al. 2022; Bohm 1992), has been detected in the circumstellar envelopes of the protoplanetary nebulae CRL 618 (Cernicharo et al. 2001) and V353 Aur (Bernard-Salas et al. 2006), but also in meteorites (Meinshein 1963), comets (Schuhmann et al. 2019), and Titan’s atmosphere (Coustenis et al. 2007; Yoon et al. 2014). In addition, the presence of benzene has been reported on giant planets (Bézard et al. 2001). While not directly observed in cold interstellar clouds due to its lack of a dipole moment, photochemical models predict its abundance there.

Water-rich ices are key constituents of molecular dense clouds and are prevalent throughout the Solar System. These ices serve as reservoirs where a large fraction of aromatic species, including benzene, are expected to freeze onto dust grains due to their low volatility. In a recent study, it was shown that the radiolytic destruction-rate constant of benzene in benzene water ice surpasses that of pure benzene ice (Tribett et al. 2026). The chemical evolution within these cosmic ices – which ultimately populates the gas phase upon sublimation in warmer regions – is fundamentally driven by external energy sources such as high-energy photons, cosmic-ray bombardment, and thermal changes. The interaction of radiation, for example (V)UV-, X-, and cosmic rays, with dense gas or ices produces excited species, ions, radicals, and electrons along the penetration tracks as the first initiating step of complex chemistry (Pimblott & LaVerne 2007; Blanco et al. 2013; McMahon & Prise 2019). While such ion/radical reactions have been studied relatively extensively (see, e.g., Snow & Bierbaum 2008; Arumainayagam et al. 2019; Öberg 2016), and the effect of UV radiation (often generated by cosmic rays exciting H2 in a process called cosmic-ray-induced photochemistry) is accounted for, the primary synthesis pathway in cold ices may be dominated by a different process. In dense cloud environments, the rate of UV production from the Lyman–Werner band of excited H2 is often considered too low to efficiently drive reactions (Prasad & Tarafdar 1983). In contrast, Galactic cosmic rays generate a massive flux of ballistic secondary electrons as they pass through the ice1.

The role of ballistic secondary electrons in astrochemistry has only been demonstrated in the last decades (Pan et al. 2004; Boyer et al. 2016; Abdoul-Carime et al. 2022). Electron-induced processes represent a new frontier in the synthesis of complex molecules in interstellar ices (Mason et al. 2014; Arumainayagam et al. 2019). These particles are generated with an energy distribution below 15 eV (Pimblott & LaVerne 2007; Mucke et al. 2010) and are capable of initiating molecular fragmentation and rearrangement of chemical bonds through the formation of subproducts (Abdoul-Carime et al. 2024b), in the same manner as photons of the similar energy range (McMahon & Prise 2019; Bulak et al. 2013), however via different processes and efficiencies (in terms of fragmentation cross-sections). For instance, it has been shown that irradiation of acetonitrile-water films by low-energy electrons (LEEs; ∼1014 e/cm2) (Abdoul-Carime et al. 2022) and by high-density UV photons (i.e., ∼1016 photons/cm2) (Bulak et al. 2013) results in the synthesis of both methanol and glycolonitrile species, which is indicative of the effectiveness of electrons to initiate processes. It is noteworthy that low-energy (4–20 eV) electron irradiation of ammonia:acetic acid ices synthesizes glycine amino acid via radical–radical reactions that arose in the vicinity of the condensed reactants (Lafosse et al. 2006). Unlike energetic (> 20 eV) particles, LEEs can selectively dissociate individual specific molecules, as has been shown in benzonitrile:water films (Abdoul-Carime et al. 2024b). Indeed, irradiation by 3 eV electrons can only trigger reactivity by fragmenting aromatic compounds that compose the film alone. This leaves water molecules unaffected by dissociation, which only arises at energies above 6 eV.

To study the crucial synthesis of functionalized aromatics in the ice phase, we focused on phenol (C6H5OH), the simplest oxygenated aromatic molecule. In this work, we investigated the chemistry of benzene:water films irradiated by low-energy electrons (LEEs < 12 eV). While proton, UV photon (Ruiterkamp et al. 1990), and γ-beam (Kodera & Hikida 1990) irradiation of such films has been explored previously, the production of phenol was not reported. Here, we examine the effects of electron irradiation at different energies employing a combined experimental and theoretical approach. Our goal is to elucidate the fragmentation of benzene and water induced by LEEs and the subsequent reactions leading to the formation of new, more complex species, such as phenol.

2. Methods

2.1. Theoretical methods

The resonance electron attachment energies were calculated in the framework of the density-functional theory (DFT) and the time-dependent DFT (TDDFT) using a multi-basis-set TDDFT methodology (Thiam & Rabilloud 2021). The vertical electron affinity (VEA) was evaluated using DFT calculations (using the functional ωB97x Chai & Head-Gordon 2008) with the diffuse basis set aug-cc-pvtz (Kendall et al. 1992), while the anionic excitation energies were calculated using TDDFT and the cc-pvtz basis set. The latter, which did not include any diffuse function, was fully suitable to describe valence-type excitations while preventing the occurrence of intruder-discretized continuum states. Gibbs free energies of fragmentation were calculated at the ωB97x/aug-ccpvtz level at 90 K. All calculations were performed with the Gaussian16 suite of programs (Frisch et al. 2016). Pre- and postprocessing operations were performed using the graphical interface Gabedit (Allouche 2011). Calculations performed on H2O can be found in a previous paper (Abdoul-Carime et al. 2022). Here, we only provide calculations on benzene.

2.2. Experimental methods

The experimental procedure is explained in detail elsewhere (Abdoul-Carime et al. 2022). Briefly, C6H6 (2.4 mbar) and H2O (22.3 mbar) vapors were premixed at room temperature, forming an admixture of about 10% benzene and 90% water in a 27 mL mixing chamber prior to the injection into the measurement chamber at a base pressure of few 10−10 mbar; this was to be condensed onto an Au substrate held at 90 K by a closed-cycle He refrigerator. A volumetrically calibrated effusing gas quantity (MKS Baratron type 127) provided an estimate of the thickness of the deposited film. The typical thickness used here was approximately five MonoLayers (MLs) of molecules within ±40% uncertainty. A pure water film of 1 ML corresponds to a thickness of 0.25 nm (Optiz et al. 2007). It is noteworthy that, in these experiments, knowledge of the exact thickness of the film was not necessary, but the film must be sufficiently thick to avoid possible effects of the metal substrate (i.e., quenching or enhancing process) and thin enough to minimize the multiple electron scattering (i.e., the mean free path of electrons in ice films is about 3 nm Leclerc et al. 1987) that would modify the energy of the reacting electrons. A monoenergetic electron beam (a few tenths of nA, ∼0.3 cm2), generated by a trochoidal electron monochromator to provide an energy selection of ΔE ∼ 400 meV, impinged normally to the substrate for 50 minutes. The electron energy was calibrated by a fast recording of the onset of the electron transmission curve (Sanche 1979). From the charging of the film during irradiation, this onset was rescaled every 30 s until no appreciable shift was observed. Otherwise, the film would be irradiated at different electron energies, and the fragmentation process – and perhaps the subsequent chemistry – would consequently be modified. After irradiation of the film by the electron beam at a given energy, the substrate was heated at a rate of 12 K/min for thermal desorption. The desorbed neutral species were detected by recording quadrupole mass spectrometry (QMS) in the “neutral” mode (Balzer). In the present experiments, the spectrometer was set at m/z 94 for the detection of phenol molecules. Note that we also observed the products formed by H2O decomposition and reaction (namely H2O2), but they are not discussed here since they have already been considered in detail elsewhere (Pan et al. 2004). The yield of the neutral species was recorded as a function of the substrate temperature providing the so-called temperature-programmed desorption (TPD) spectrum. Each TPD spectrum was repeated from three to six times, providing the measurement fluctuations (c.a., ∼40%), which can be associated with the accuracy of the presented data.

3. Results and discussion

Temperature-programmed desorption spectra of m/z 94 u (phenol) were recorded over a range of electron irradiation energies (0–13 eV) and electron currents (0–140 nA) as illustrated in Figure 1: (a – black) no irradiation, (b – red) 5 eV, (c – blue) 7 eV, (d – brown) 8 eV, (e – green) 9 eV, and (f – purple) 13 eV. Up to electron energies of 5 eV, this species is not observed, suggesting that it is not formed upon electron irradiation. From 6 to 10 eV, a feature is observed, peaking at 166 K, while disappearing for higher electron energies. TPD temperatures of pure phenol deposited onto Pt(111) and Ag(111) were measured to be 195 K (Ihm & White 2000) and 204 K (Lee et al. 2001), while that of H2O from pure-water-ice adsorption on polycrystalline Au substrate was been reported to be 160 K (Collings et al. 2004). As the desorption temperature of phenol coincides with that of pure water, it seems that phenol molecules are mostly synthesized from benzene “embedded” in water ice rather at the gold surface. Thus, formed phenol molecules are expelled along with desorbed water molecules (Smith et al. 1997). The TPD peak is then integrated and normalized to the electron current (also convertible to electron dose for 50 min irradiation), for each irradiating energy. This yield, plotted as the function of the electron energy (Figure 2), presents a resonant feature at the electron energy of about 7 eV. This measured yield function is notably “sharply peaked” (6–9 eV) in contrast to our previous work on electron irradiation of benzonitrile:water experiments performed at the same experimental conditions (Abdoul-Carime et al. 2024a). A broad structure in the 6–12 eV energy range, in addition to a sharp peak at 2 eV in the phenol yield function, was indeed reported.

Thumbnail: Fig. 1. Refer to the following caption and surrounding text. Fig. 1.

Temperature-programmed desorption spectra of m/z 94 u (phenol) recorded after depositing a fresh film (a – black); 50 min electron irradiation at (b – red) 5 eV–50 nA, (c – blue) 7 eV–50 nA, (d – brown) 8 eV–133 nA, (e – green) 9 eV–91 nA and (f – purple) 13 eV–120 nA. The dashed line is a guides the eye.

Thumbnail: Fig. 2. Refer to the following caption and surrounding text. Fig. 2.

Integrated phenol (C6H5OH) yield normalized to the electron current as the function of the electron energy. The error bars are estimated to be 40% (see experimental method).

Previous experiments on low-energy electron induced synthesis in two-reactant films (Abdoul-Carime et al. 2024a) have shown that at the energies below the typical ionization potential of most organic molecules (i.e., below 8–9 eV), the reactions are initiated by the fragmentation of specific molecules via dissociative electron attachment (DEA) (Illenberger & Momigny 1999). Briefly, the impinging free electron is initially captured by a molecule, forming a transient anion. The latter decays into dissociation for a negative anion fragment and at least one neutral counterpart. If the neutral fragment is a reactive radical, subsequent reactions may take place between the radical and the neighbouring molecules (Abdoul-Carime et al. 2024a; Abdoul-Carime & Kopyra 2025). The formation of the transitory negative ion arises either from (1) a shape (i.e., accommodation of the extra electron in a usually unoccupied molecular orbital (MO)) or (2) a core-excited resonance (i.e., the excitation of a valence electron in some excited state concomitantly to the capture of the extra electron by the molecular positive core). A third possibility is when DEA is mediated by the formation of a dipole-bound anion. This latter has been observed in the gas phase (Abdoul-Carime et al. 2024c), but it is unlikely formed in the condensed phase. Indeed, the dipole-bound character of the anion produced in isolation is lost in the presence of other interacting molecules (Desfrançois et al. 1995). DEA to H2O has been well studied experimentally in the gas phase (Rawat et al. 2007), in molecular films (Pan et al. 2005), and theoretically (Abdoul-Carime et al. 2022; Faure et al. 2004; Lacombe et al. 2015). The dominant dissociation channel (by far) consists of the resonant production of the H− anion in association with an OH• radical at 7 eV and a threshold at round 6 eV (Rawat et al. 2007). Further fragmentation peaks have been reported at 9.2 eV and 12.6 eV (Rawat et al. 2007). The observed core-excited resonances implicate LUMO or LUMO+1 ← HOMO or HOMO-1 transitions concomitantly to the capture of the electron by the positive molecular core (Abdoul-Carime et al. 2022). For benzene, the gas-phase DEA experiments showed the resonant cleavage of the C–H bond for C6H 5 − Mathematical equation: $ _{5}^{-} $ anion and •H radicals, as well as the fragmentation of the aromatic ring producing C2H 2 − Mathematical equation: $ _{2}^{-} $ anion at electron energies of around 8 eV and 9 eV (Fenzlaff & Illenberger 1984).

It was recently shown that the irradiation of benzene films by 10–1000 eV electrons produced H− anions as the dominant anion fragment (Alvarez et al. 2024). In fact, for most hydrocarbon and aromatic molecules, electron-stimulated desorption from thin film experiments has shown that the production of the hydrogen anion is by far the dominant dissociation channel detectable (e.g., Rowntree et al. 1991; Ellis-Gibbings et al. 2017). The resonant features observed in DEA to benzene experiments (Fenzlaff & Illenberger 1984) are closely associated with the calculated resonances presented in Figure 3. Notably, the calculated resonances reflect the transition states, while the peak positions in experimental measurements are the convolution of the attachment cross-sections (i.e., MOs) and the energy-dependent survival probability (Illenberger & Momigny 1999). The shape-resonance energies at 1.58, 1.68, and 5.5 eV (shaded in gray, Figure 1) agree with the R-matrix-calculated electron scattering cross-sections and the gas-phase experimental transmission experiments (Costa et al. 2019). Above 5.5 eV, our theory presents core-excited resonances consisting of the excitation of a core (valence) electron to some higher energy empty states. More interestingly, the MO transition is strongly electron-spin dependent (↑ and ↓ are electron-spin up and down states, respectively). Indeed, the π5 ← π3 transition energy depends on the spin electron transition: 6.8 eV and 7.64 eV for ↓ and ↑ electrons, respectively. The 8.60 eV, 9.22 eV, and higher resonances are associated with the linear combination of up and down spin electrons. It is to be noted that π states are non-dissociative unless this state crosses a dissociative σ* state leading to the production of the negative fragments and their associated neutral counterparts; two asymptotic σ* states were found to lead to C6H 5 − Mathematical equation: $ _{5}^{-} $ or H− anion fragments, respectively (Figure 4). Gas-phase experiments on DEA with benzene have shown that the production of C2H 2 − Mathematical equation: $ _{2}^{-} $ possibly generated neutral C4H4 (Fenzlaff & Illenberger 1984); the latter species may be a bi-radical or, most likely, a stable, closed-shell molecule with m/z 52 with linear (e.g., HC≡C–C(H) = CH2) or cyclic structures (Cremer et al. 2006). The present work has not clearly identified any species at m/z in the vicinity of 69 u or 86 u, associable with either C4H4OH or C4H4OH2 compounds, respectively.

Thumbnail: Fig. 3. Refer to the following caption and surrounding text. Fig. 3.

Calculated attachment energies (in eV) relative to the neutral ground state of C6H6 are given together with the molecular orbitals involved in the trapping of the extra electron. The formation of this transitory anion arises from either the shape resonance (the orbital occupied by the extra electron is plotted on a gray background) or core-excited resonances when the trapping of the colliding electron into the LUMO occurs concomitantly with the promotion of a valence electron. The arrows indicate the spin of the implicated electron (↑ up, ↓ down), and “→” shows the transition.

Thumbnail: Fig. 4. Refer to the following caption and surrounding text. Fig. 4.

Adiabatic potential energy curves (PEC) of the anion C6H 6 − Mathematical equation: $ _{6}^{-} $ calculated at the ωB97x/6-31G level. Two asymptotic σ* states are found to lead C6H 5 − Mathematical equation: $ _{5}^{-} $ or H− fragments, respectively. The orbital occupied by the extra electron is shown when the C–H bond elongation is equal to 3 Å.

As the H− anion is the most dominant fragment from the interaction of LEEs with both H2O and C6H6, the concomitantly produced OH• and C6H 5 ∙ Mathematical equation: $ _{5}^{\bullet} $ radicals may interact either together, or with water or benzene molecules yielding phenol: C6H5OH (m/z 94). It is interesting to note here that the yield function shown in Figure 2 resembles to that of H−/benzene (Fenzlaff & Illenberger 1984) (narrow energy resonance) and thus corroborates the key role played by the OH• + C6H 5 ∙ Mathematical equation: $ _{5}^{\bullet} $ radical reaction.

Table 1 displays gas-phase-calculated energetics of possible secondary reactions by providing the Gibbs free energies. In the water-ice matrix, the exoergicity is expected to remain close to its gas-phase value, while barrier heights of transition states and intermediates might be slightly lowered or raised. Reaction (1), OH• + C6H 5 ∙ → Mathematical equation: $ _{5}^{\bullet}\,{\rightarrow} $ C6H5OH, was calculated to be very exoergic by 4.6 eV. While reaction (2), OH• + C6H6 → C6H5OH, is found endoergic by 51 meV, reaction (3), C6H 5 ∙ Mathematical equation: $ _{5}^{\bullet} $ + H2O → C6H5OH, is unlikely within the present experimental conditions, since it requires additional energy of ∼260 meV to be activated. Reaction (1) may proceed via dissipation of the excess energy in the water-ice matrix or via the release of a UV photon not detectable by the present setup. While reaction (2) appears to be almost energetically accessible a priori, the process nevertheless requires a potential barrier of ∼0.5 eV to be overcome (Hollman et al. 2011). Therefore, this reaction channel is not likely in the present experimental conditions.

Table 1.

Calculated Gibbs free energy (eV) at 90 K for the formation of phenol.

The yield of production of phenol can be compared to that of the benzene in the c-C6H6/H2O film deposited in the substrate. The number of ions, Nion, of C6H 6 + Mathematical equation: $ _{6}^{+} $ and C6H5OH+ measured by the 70 eV electron ionization in the mass spectrometer can be estimated as Nion ∼ NmolNeσmolϵ, where Nmol is the number of molecules, Ne the density of the ionizing electrons, σmol the ionization cross-section, and ϵ the collection efficiency. As 70 eV electron ionization cross-sections of benzene and phenol have been estimated to be 26.7 Å2 (Singh et al. 2016) and 17.5 Å2 (Gupta et al. 2019), respectively, from the present measurement of N phenol + / N benzene + ∼ 0.52 % Mathematical equation: $ N^{+}_{\mathrm{phenol}}/N^{+}_{\mathrm{benzene}}\sim0.52\% $ per μA electron current during a 50 min irradiation, we can estimate the production of phenol from benzene, Nphenol/Nbenzene, to be about 2.6 × 10−4 per μC. The formation rate of phenol via the irradiation of the (10:90%) benzene:water film can be compared to a certain degree to that from the (4:96%) benzonitrile:water film (Abdoul-Carime et al. 2024a). For the latter, for 3 eV electron irradiation, this rate has been evaluated to be ∼4.10−4/μC per irradiated surface.

4. Conclusions

Past studies have shown that UV photolysis of PAHs in water ice leads to the replacement of peripheral H atoms by OH groups (Bernstein et al. 2002). In contrast, for the simplest aromatic hyrdocarbon, i.e., benzene, only O-heterocyclic benzene is clearly formed under UV irradiation of benzene–water ice, while phenol is tentatively detected (Materese et al. 2015). However, it has been shown that phenol can be generated in water–benzene systems via various pathways including catalytic conversion of benzoic acid (Fraga-Dubreuil et al. 2006), a radical–neutral C6H6 + OH• reaction well above 300 K (Baulch et al. 2005), and the photolysis of a benzene and ozone mixture in argon matrices (C6H6 + O3 + hν (> 280 nm) → C6H6 + •O(3P) Parker & Davis 1999).

We demonstrate that the irradiation of benzene molecules in a water-ice environment by low-energy (< 12 eV) electrons also leads to the synthesis of phenol. The initial step consists of electron-induced dissociation of H2O and C6H6, yielding OH• and C6H 5 ∙ Mathematical equation: $ _{5}^{\bullet} $ neutral radicals, respectively. Three subsequently different processes involving neutral radicals, respectively OH• and C6H 5 ∙ Mathematical equation: $ _{5}^{\bullet} $, are underlined: (1) OH• + C6H 5 ∙ Mathematical equation: $ _{5}^{\bullet} $, (2) OH• + C6H6, and (3) C6H 5 ∙ Mathematical equation: $ _{5}^{\bullet} $ + H2O. In photolysis benzene/O3 in argon matrix experiments (Parker & Davis 1999), the O• radical may diffuse in the solid for a reaction. In the present work, we found that phenyl and hydroxyl radicals may also possibly diffuse before reacting since the deposited vapors, mainly containing water molecules, form amorphous ices (i.e., amorphous ice below 105 K and a crystalline structure above 120 K (Spisa et al. 2001). However, the structure of films may affect reactivity (Ghesquière et al. 2018; Garrod et al. 2022). Among the three mentioned processes, only (1) is energetically accessible. The present observations may be relevant in the context of reactions in meteorites (e.g., Tagish lake Hilts et al. 2014, Murchinson, or Orgueil Derenne & Robert 2010) and, more broadly, to the chemistry of icy cores (Ghosh et al. 2022).

By showing that the functionalization of an aromatic species can be driven out by low-energy electrons, our study supports the view that Galactic cosmic rays characterized by energies above ∼1010 eV, triggering a cascade of low-energy electrons (≤20 eV) when impacting interstellar ices, can be a significant contributor (Wu et al. 2024) to the interstellar synthesis of prebiotic molecules whose delivery by comets, meteorites, and interplanetary dust particles may have kick-started life on Earth. Furthermore, it is desirable to incorporate low-energy electron-induced processes in current and future astrochemical simulation toolkits not only for water ices (Shingledecker et al. 2020), but more generally for cosmic ices (Wakelam et al. 2013). Such models are important for interpreting James Webb Space Telescope observations, which are currently being used to probe complex organic molecules found in ices near star-forming regions in the context of the interstellar heritage of the building blocks of life.

Acknowledgments

This study and the visit of E.O. and S.C. were supported by CNRS MITI – “Conditions Extrêmes 2024” (grant number 265810). In addition, F.R. thanks the GENCI-IDRIS for supporting the computing time through the grant A0150807662.

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1

105 electrons/MeV deposited: International Commission on Radiation Units and Measurements, Report 31. Average energy required to produce an ion pair, Bethesda, MD (1979).

All Tables

Table 1.

Calculated Gibbs free energy (eV) at 90 K for the formation of phenol.

In the text

All Figures

Thumbnail: Fig. 1. Refer to the following caption and surrounding text. Fig. 1.

Temperature-programmed desorption spectra of m/z 94 u (phenol) recorded after depositing a fresh film (a – black); 50 min electron irradiation at (b – red) 5 eV–50 nA, (c – blue) 7 eV–50 nA, (d – brown) 8 eV–133 nA, (e – green) 9 eV–91 nA and (f – purple) 13 eV–120 nA. The dashed line is a guides the eye.
In the text
Thumbnail: Fig. 2. Refer to the following caption and surrounding text. Fig. 2.

Integrated phenol (C6H5OH) yield normalized to the electron current as the function of the electron energy. The error bars are estimated to be 40% (see experimental method).
In the text
Thumbnail: Fig. 3. Refer to the following caption and surrounding text. Fig. 3.

Calculated attachment energies (in eV) relative to the neutral ground state of C6H6 are given together with the molecular orbitals involved in the trapping of the extra electron. The formation of this transitory anion arises from either the shape resonance (the orbital occupied by the extra electron is plotted on a gray background) or core-excited resonances when the trapping of the colliding electron into the LUMO occurs concomitantly with the promotion of a valence electron. The arrows indicate the spin of the implicated electron (↑ up, ↓ down), and “→” shows the transition.
In the text
Thumbnail: Fig. 4. Refer to the following caption and surrounding text. Fig. 4.

Adiabatic potential energy curves (PEC) of the anion C6H 6 − Mathematical equation: $ _{6}^{-} $ calculated at the ωB97x/6-31G level. Two asymptotic σ* states are found to lead C6H 5 − Mathematical equation: $ _{5}^{-} $ or H− fragments, respectively. The orbital occupied by the extra electron is shown when the C–H bond elongation is equal to 3 Å.
In the text

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