Search

We found that electron attachment to the van der Waals complex (O2···CO2) turns the weak intermolecular bond into a pseudochemical bond of significant strength. The resulting monomeric molecular anion (O2-CO2)- may be a form of CO4-, the gaseous anionic species suspected to be present in Earth's ionosphere whose chemical characteristics have not been comprehensively identified since its existence was first predicted by Conway in 1962. The measured vertical detachment energy of CO4- is very large (4.56 ± 0.05 eV), while the known electron affinity of its component species is much smaller (0.448 eV, O2) or even negative (-0.6 eV, CO2). These characteristics are correctly borne out by theoretical calculations that show that electron attachment transforms the van der Waals complex to a single contiguous molecular anion, with the formation of a pseudochemical bond between O2 and CO2 through an extended π-orbital system.

We investigate dissociative electron attachment to 5-fluorouracil (5-FU) employing a crossed electron-molecular beam experiment and quantum chemical calculations. Upon the formation of the 5-FU− anion, 12 different fragmentation products are observed, the most probable dissociation channel being H loss. The parent anion, 5-FU−, is not stable on the experimental timescale (~140 µs), most probably due to the low electron affinity of FU; simple HF loss and F− formation are seen only with a rather weak abundance. The initial dynamics upon electron attachment seems to be governed by hydrogen atom pre-dissociation followed by either its full dissociation or roaming in the vicinity of the molecule, recombining eventually into the HF molecule. When the HF molecule is formed, the released energy might be used for various ring cleavage reactions. Our results show that higher yields of the fluorine anion are most probably prevented through both faster dissociation of an H atom and recombination of F− with a proton to form HF. Resonance calculations indicate that F− is formed upon shape as well as core-excited resonances.

In this work we present an ab initio investigation into the effect of monohydration on the interaction of uracil with low energy electrons. Electron attachment and photodetachment experimental stud...

Our experimental progresses on the reaction dynamics of dissociative electron attachment (DEA) to carbon dioxide (CO2) are summarized in this review. First, we introduce some fundamentals about the DEA dynamics and provide an epitome about the DEAs to CO2. Second, the experimental technique developments are described, in particular, on the high-resolution velocity map imaging apparatus in which we put a lot of efforts during the past two years. Third, our findings about the DEA dynamics of CO2 are surveyed and briefly compared with the others’ work. At last, we give a perspective about the applications of the DEA studies and highlight the inspirations in the production of molecular oxygen on Mars and the catalytic transformations of CO2.

Efficient radiotherapy requires the concomitant use of ionizing radiation (IR) and a radiosensitizer. In the present work uracil-5-yl O-sulfamate (SU) is tested against its radiosensitizing potenti...

9 pags., 5 figs., 1 tab. -- This article is part of the Research Topic: Electron and positron scattering and spectroscopic studies of molecular species of applied interest and importance, We have used a crossed electron molecular beam setup to investigate the behavior of the anticancer drug temozolomide (TMZ) upon the attachment of low-energy electrons (0–14 eV) in the gas phase. Upon a single electron attachment, eight anionic fragments are observed, the most intense being an anion with mass of 109 u at a resonance energy of 0 eV. Quantum chemical calculations suggest that this ion is generated after the tetrazine ring opens along a N–N bond and its fragments leave the molecule, forming an imidazole-carboxamide species. This ion represents the most abundant fragment, with further fragments following from its dissociation. The tetrazine ring cleavage reaction forming N is thus the driving force of TMZ reactivity upon electron attachment., SD acknowledges funding support by the Austrian Science Fund (FWF), Vienna (P30332). The computational results presented have been achieved using the HPC infrastructure LEO of the University of Innsbruck. CG and GG acknowledge partial financial support from the Spanish Ministerio de Ciencia e Innovación (Project PID2019-104727RB-C21) and CSIC (Project LINKA20085).

Investigation of microwave-activated CH4/H2 plasma used in chemical vapour deposition of diamond revealed the presence of electronically excited C2−∗ (B2Σu+). Using high-level electronic structure ...

We have investigated the electron-attached states in Watson-Crick guanine-cytosine and adenine-thymine base pairs using the highly accurate equation-of-motion coupled-cluster (EOM-CC) method and extended basis sets. Both base pairs have two bound anionic states. The dipole-bound state is stable even at the neutral geometry, but the valence-bound state is only adiabatically bound. The initial electron attachment results in the formation of a dipole-bound state that acts as a doorway to the valence-bound anionic state. The adiabatic potential energy surface of ground and first excited states of an anion shows an avoided crossing, indicating mixing of the electronic and nuclear degrees of freedom. We have calculated the coupling strength between the valence- and dipole-bound states by fitting a simple diabatic model potential to a cut through the two adiabatic surfaces of the anions obtained from the EOM-CC calculations. The transfer of the electron from the initial dipole-bound to the final valence-bound state has been found to happen at an ultrafast time scale.

Dissociative electron attachment to 2-chlorotoluene has been studied experimentally. The formed Cl− fragment appears in the energy range from 0 to 2 eV. Increasing the temperature of the target molecule results in a decrease of the height of the threshold peak (∼0 eV) but in a considerable increase of the height of the second peak at 0.78 eV. Such behaviour was observed only rarely and does not occur in similar molecules. We have analysed the out-of-plane vibrations and calculated approximate potential energy curves for the neutral and anionic states. Possible explanations of the observed temperature dependence are discussed.

The complete dissociation dynamics of low energy electron attachment to the ammonia molecule has been studied using velocity slice imaging (VSI) spectrometry. One low energy resonant peak around 5.5 eV and a broad resonance around 10.5 eV incident electron energies have been observed. The resonant states mainly dissociate via H- and NH2- fragments, though for the upper resonant state, the signature of NH- fragments is also predicted due to a three-body dissociation process. Kinetic energy and angular distributions of the NH2- fragment anions are measured simultaneously around the two resonances. Based on our experimental observations, we conclude that a temporary negative ion (TNI) state with A1 symmetry is responsible for the lower resonance. Whereas, we find strong evidence for the existence of a TNI state having A1 symmetry at the 10.5 eV resonance for the first time.

We probe the negative ion production upon the interaction of free electrons with gas-phase HNO3 and its mixed clusters with water. The electron-induced chemistry changes strongly with clustering, exhibiting significant electron energy dependence. For HNO3 hydrates, we identified three involved energy ranges with different behavior: low energies up to about 3.5 eV, an intermediate energy range around 6 eV, and a high energy range, approximately above 9 eV. The major difference is the degree to which the major gas-phase product, NO2-, is converted to NO3-. The latter is the dominant stratospheric anion. Its appearance due to the electron interaction with mixed HNO3/water ice particles thus strongly depends on the electron energy. We discuss the elementary processes and reaction pathways behind the anion conversion.

The incorporation of modified uracil derivatives into DNA leads to the formation of radical species that induce DNA damage. Molecules of this class have been suggested as radiosensitizers and are still under investigation. In this study, we present the results of dissociative electron attachment to uracil-5-yl O-(N,N-dimethylsulfamate) in the gas phase. We observed the formation of 10 fragment anions in the studied range of electron energies from 0–12 eV. Most of the anions were predominantly formed at the electron energy of about 0 eV. The fragmentation paths were analogous to those observed in uracil-5-yl O-sulfamate, i.e., the methylation did not affect certain bond cleavages (O-C, S-O and S-N), although relative intensities differed. The experimental results are supported by quantum chemical calculations performed at the M06-2X/aug-cc-pVTZ level of theory. Furthermore, a resonance stabilization method was used to theoretically predict the resonance positions of the fragment anions O− and CH3−.

Efficient new codes enabling double electron-attachment equation-of-motion coupled-cluster (DEA-EOMCC) calculations with up to 4-particle���2-hole (4p-2h) excitations, treated with active orbitals, have been developed. They can be applied to medium size diradicals using larger basis sets and modest computational resources. The new codes have been used to determine the singlet���triplet (S���T) gaps characterising the ortho-, meta-, and para-benzyne isomers using the correlation consistent cc-pVxZ basis sets with x=D, T, and Q and complete-basis-set (CBS) extrapolations. Our best estimates of the S���T gaps in the ortho-, meta-, and para-benzynes obtained in the DEA-EOMCC calculations with an active-space treatment of 4p-2h terms, extrapolated to the CBS limit and corrected for vibrations, are 37.4, 20.7, and 4.5 kcal/mol, respectively, in excellent agreement with experiment.

To advance our quest to understand the role of low energy electrons in biomolecular systems, we performed investigations on dissociative electron attachment (DEA) to gas-phase N-ethylformamide (NEF) and N-ethylacetamide (NEA) molecules. Both molecules contain the amide bond, which is the linkage between two consecutive amino acid residues in proteins. Thus, their electron-induced dissociation can imitate the resonant behavior of the DEA process in more complex biostructures. Our experimental results indicate that in these two molecules, the dissociation of the amide bond results in a double resonant structure with peaks at ∼5 eV and 9 eV. We also determined the energy position of resonant states for several negative ions, i.e., the other dissociation products from NEF and NEA. Our predictions of dissociation channels were supported by density functional theory calculations of the corresponding threshold energies. Our results and those previously reported for small amides and peptides imply the fundamental nature for breakage of the amide bond through the DEA process.

2,3,6,7,10,11-Hexabromotriphenylene (HBTP) and 2,3,6,7,10-pentabromotriphenylene (PBTP) were investigated by means of dissociative electron attachment spectroscopy (DEAS). The dominant decay channel of the transient molecular negative ions consists of elimination of Br– with resonances in the low electron energy region. Formation of long-lived parent anions with autodetachment lifetime τa = 310 μs is observed at thermal electron energies. The adiabatic electron affinities, EAa = 1.12 ± 0.1 eV in HBTP and 1.09 ± 0.1 eV in PBTP, evaluated using a simple Arrhenius approach are in good agreement with those predicted by DFT (XYG3/Def2-TZVPP//PBE0/Def2-TZVPP) calculations.

Dissociative electron attachment is a mechanism found in a large area of research and modern applications. This process is initiated by a resonant capture of a scattered electron to form a transitory anion via the shape or the core-excited resonance that usually lies at energies above the former (i.e., >3 eV). By studying experimentally and theoretically the interaction of nickel(II) (bis)acetylacetonate, Ni(II)(acac)2, with low energy electrons, we show that core-excited resonances are responsible for the molecular dissociation at unusually low electron energies, i.e., below 3 eV. These findings may contribute to a better description of the collision of low energy electrons with large molecular systems.

We present a method for locating non-Hermitian degeneracies, called exceptional points (EPs), and minimum-energy EPs between molecular resonances using the complex absorbing potential equation-of-motion coupled-cluster (CAP-EOM-CC) method. EPs are the complex-valued analogue of conical intersections (CIs) and have a similar impact on nonadiabatic processes between resonances as CIs have on nonradiative transitions between bound states. We demonstrate that the CAP-EOM-CC method in the singles and doubles approximation (CAP-EOM-CCSD) yields crossings of the correct dimensionality. The use of analytic gradients enables applications to multidimensional problems. Results are presented for hydrogen cyanide and chloroethylene, for which the location of the crossings of anionic resonances is crucial for understanding the dissociative electron attachment process.

Small molecular species present in mitochondria as, e.g., quinones and oxygen, can capture cellular electrons thus behaving as electron carriers or reactive species, supporting the fundamental process of respiration, and providing protection from pathogens. When xenobiotics penetrate living cells, their delicate redox balance can be altered by capture of cellular electrons to form temporary negative ions. The latter can give rise to the formation of reactive species via dissociative electron attachment (DEA), as observed under gas-phase or electrochemical conditions. DEA to isolated biorelevant molecules studied in vacuo with the support of in silico methods can serve as a model to predict the behavior of these species in vivo under conditions of electron “leakage” in the lipid-protein-cytosol media or in enzymatic active centers. The present review summarizes the results of studies on the correlation between the biological activity of various classes of compounds and fragment species formed by DEA. The following classes of compounds are included into the present review: chlorinated organic pollutants, brominated ethers, captafol and 2,6-dichloroisonicotinic acid, atrazine and bromoxynil, non-steroidal anti-inflammatory drugs, natural polyphenolic compounds, anthralin, salicylic acid and related compounds, ascorbic acid, melatonin, tryptophan, indole and related compounds and some organic peroxides. Formation of temporary molecular anions and their decay are characterized using electron transmission spectroscopy (ETS) and DEA spectroscopy. Quantum-chemical calculations support the identification of the dissociation products. Cellular electron attachment to unnatural electron acceptors is likely to be the first step of cascade processes which constitute the molecular mechanisms of electron-driven biological processes. The fragment species detected with DEA are of importance for understanding the metabolism of xenobiotics, including side effects produced by drugs.

Considering the fact that the efficiency of the uridine-5-methyl radical in producing cytotoxic DNA intrastrand cross-link lesions is greatly higher than that of the uridine-5-yl radical, the radiosensitizing action of 5-(halomethyl)uridines (5-XCH2U, X = F, Cl, or Br) is studied in the present work. It is found that 5-XCH2U has sufficient electron affinity to capture a pre-hydrated or a hydrated electron, and electron attachment leads to significantly facile X− elimination forming the uridine-5-methyl radical. All these three halogenated uridine derivatives are shown to be potential radiosensitizers, with their radiosensitizing abilities increased in an order 5-FCH2U

Polyanionic lead clusters have been produced by electron attachment in a Penning trap. The smallest dianionic and trianionic lead clusters observed were of size n = 28 and n = 69, respectively and the appearance sizes following the definition of Martinez et al. (2015) are n = 39 and n = 80, respectively. In addition, and in contrast to previous measurements on clusters of several other metals, decay reactions are observed in the cluster size range of n = 14–49. The decay products are similar, but not identical, to those reported for the photodissociation of Pb n − .

Molecular rotors at surfaces are of current interest. Here we employ molecular dynamics to examine rotation in the chemisorbed product, meta-iodophenyl, from electron-induced reaction of meta-diiodobenzene at a noble metal (M(1 1 0)). Electron attachment gives iodophenyl that rotates unidirectionally ('clockwise') around a carbon-metal (C-M) 'pivot bond', due to I-M attractions. Mobility is enhanced by tilting the phenyl. During rotation the I-atom of iodophenyl bounces off successive M-atoms. As M changes from Cu to Ag to Au, the surface increasingly damps the bounce, diminishing rotation. Reconstruction of the gold can cause the atomic pivot-point to shift substantially, thereby giving opposite 'anticlockwise' rotation.

Here we present a combined experimental and theoretical study on the fragmentation of o- and p-tetrafluorohydroquinone upon low energy electron attachment. Despite an identical ring-skeleton and identical functional groups in these constitutional isomers, they show distinctly different fragmentation patterns, a phenomenon that cannot be explained by distinct resonances or different thermochemistry. Using high-level quantum chemical calculations with the computationally affordable domain localized pair natural orbital approach, DLPNO–CCSD(T), we are able to provide a complete and accurate description of the respective reaction dynamics, revealing proton shuttling and transition states for competing channels as the explanation for the different behavior of these isomers. The results represent a “schoolbook example” of how the combination of experiment and modern high-level theory may today provide a thorough understanding of complex reaction dynamics by computationally affordable means., (This work was supported by the Icelandic Center of Research (RANNIS) Grant No. 13049305 and 141218051 and the University of Iceland Research Fund.

In this study we present an investigation of the negative ion-molecule chemistry of pentachloroethane (PCE) in air based ion mobility spectrometry and ion mobility spectrometry–mass spectrometry systems. The observed product ions are Cl − , produced by dissociative electron attachment, and Cl − ·HOO resulting from a reaction with O 2 − . Based upon the moisture content of the system, these ions can be observed as a doublet in a ‘dry’ system or as a singlet in a ‘wet’ system. The nature of the Cl − ·HOO product ion was investigated by using isoflurane (ISOF) as a probe to monitor the changing ratios of Cl − and Cl − ·HOO as the PCE concentration decreased. This confirmed the origins of the two product anions. Electronic structure calculations are provided. These have aided the understanding of the reaction processes observed.

This paper reports the measurements of the rate coefficients and the activation energies of the electron capture processes with various chlorinated alkenes. The electron attachment processes in the mixtures of chlorinated alkenes with carbon dioxide have been investigated using a Pulsed Townsend technique. This study has been performed in the temperature range (298–378) K. The obtained rate coefficients more or less depended on temperature in accordance to Arrhenius equation. The activation energies ( E a ’s) were determined from the fit to the experimental data points with function ln( k ) = ln( A ) − E a / k B T . The rate coefficients at 298 K were equal to 1.0 × 10 −10 cm 3 s −1 , 2.2 × 10 −11 cm 3 s −1 , 1.6 × 10 −9 cm 3 s −1 , 4.4 × 10 −8 cm 3 s −1 , 2.9 × 10 −12 cm 3 s −1 and 7.3 × 10 −12 cm 3 s −1 and activation energies were: 0.27 eV, 0.26 eV, 0.25 eV, 0.21 eV, 0.55 eV and 0.42 eV, for trans -1,2-dichloroethylene, cis -1,2-dichloroethylene, trichloroethylene, tetrachloroethylene, 2-chloropropene, 3-chloropropene respectively.

The stabilization method is used in conjunction with the equation-of-motion electron-attachment coupled-cluster method to calculate the complex energies of the 2 P temporary anion states of Be and Mg as well as of the 2 D temporary anions states of Mg and Ca. The calculated resonance parameters for the 2 P state of Mg − and 2 D state of Ca − agree well with experiment. Experimental results are not available for the 2 P anion of Be, but we note that our calculated resonance parameters of 2 P Be − , while in good agreement with the CI results of McNutt and McCurdy (1983), differ significantly from the results of two other recent theoretical studies.

Misonidazole (MISO) was considered as radiosensitizer for the treatment of hypoxic tumors. A prerequisite for entering a hypoxic cell is reduction of the drug, which may occur in the early physical-chemical stage of radiation damage. Here we study electron attachment to MISO and find that it very effectively captures low energy electrons to form the non-decomposed molecular anion. This associative attachment (AA) process is exclusively operative within a very narrow resonance right at threshold (zero electron energy). In addition, a variety of negatively charged fragments are observed in the electron energy range 0&ndash, 10 eV arising from dissociative electron attachment (DEA) processes. The observed DEA reactions include single bond cleavages (formation of NO2&minus, ), multiple bond cleavages (excision of CN&minus, ) as well as complex reactions associated with rearrangement in the transitory anion and formation of new molecules (loss of a neutral H2O unit). While any of these AA and DEA processes represent a reduction of the MISO molecule, the radicals formed in the course of the DEA reactions may play an important role in the action of MISO as radiosensitizer inside the hypoxic cell. The present results may thus reveal details of the molecular description of the action of MISO in hypoxic cells.

Electron attachment to the 3-benzelidenephthalide and phenolphthalein molecules and decay channels of their molecular anions were investigated by means of Dissociative Electron Attachment (DEA) spectroscopy and Electron Transmission Spectroscopy (ETS). Interpretations of these experimental data were supported with UV-spectroscopy and DFT calculations. The average electron detachment times for the long-lived molecular anions of 3-benzelidenephthalide and phenolphthalein were measured to be 150 microseconds at 120 °C and 560 microsecondsat 190 °C, respectively. The long-lived molecular anions of phenolphthalein are ascribed to an isomer formed by ring opening. The present results suggest that, oppositely to phenolphthalein, polymeric materials based on 3-benzylidenephthalide cannot be switched to a high conductive state due to different mechanisms of stabilization of their long-lived molecular anions.

We probe the electron attachment in hexafluoropropylene oxide, C3F6O, a gas widely used in plasma technologies. We determine the absolute electron attachment cross section using two completely different experimental approaches: (i) a crossed-beam experiment at single collision conditions (local pressures of 5x10-4 mbar) and (ii) a pulsed Townsend experiment at pressures of 20 - 100 mbar. In the later method, the cross sections are unfolded from the electron attachment rate coefficients. The cross sections derived independently by the two methods are in very good agreement. We additionally discuss the dissociative electron attachment fragmentation patterns and their role in the radical production in industrial HFPO plasmas., The Journal of Chemical Physics, 149 (20), ISSN:0021-9606, ISSN:1089-7690

Dissociative electron attachments to OCS with the attachment energies of 4.3, 4.7, 5.0, 6.2, 6.5, 6.8, and 7.0 eV are investigated by measuring the S − momentum distributions with time-sliced anion velocity image mapping technique. In this energy range, the ground-state fragmentation, e − + OCS → CO( X ˜ 1 Σ+) + S − (2Pu), is only one dissociation pathway allowed in energy. All velocity images show the predominant feature of the low-speed S − ions, but the middle- and high-speed S − ions appear at the higher attachment energies (6.2–7.0 eV). The trimodel speed distribution of S − ion should be attributed to the different populations of the rovibrational states of CO fragment, however, the dynamic details of above dissociations are still unclear and demand theoretical calculations.

Although 5-bromo-2'-deoxyuridine (5BrdU) possesses significant radiosensitizing power in vitro, clinical studies do not confirm any advantages of radiotherapy employing 5BrdU. This situation calls for a continuous search for efficient radiosensitizers. Using the proposed mechanism of radiosensitization by 5BrdU, we propose a series of 5-substituted uracils, XYU, that should undergo efficient dissociative electron attachment. The DFT-calculated thermodynamic and kinetic data concerning the XYU degradations induced by electron addition suggests that some of the scrutinized derivatives have much better characteristics than 5BrdU itself. Synthesis of these promising candidates for radiosensitizers, followed by studies of their radiosensitizing properties in DNA context, and ultimately in cancer cells, are further steps to confirm their potential applicability in anticancer treatment.

The prototype dithiolene (ethane-1,2-dithione; dithioglyoxal) constitutes the core component of metal-dithiolene complexes whose studies have burgeoned during the past half of a century in interdisciplinary research fields ranging from material sciences to enzymology. The recent vigorous research activity owes much to the works in the incubating period of the 1960s. However, due to the extreme reactivity of dithiolenes, basic studies on their electronic structure are conspicuously meager. In this paper, we report the electronic absorption spectrum of the radical anion in the title together with quantum chemical analyses on its electronic structure and the molecular geometry. As a result, the experimental result is consistently accounted for. We expect the results to be helpful for further understanding the electronic structure and reactivity of metal-dithiolene complexes.

Electron attachment to phosphoryl chloride (phosphorus oxychloride) POCl 3 has been studied in the gas phase by mass spectrometry at several low temperatures (47.7, 74.5, 169.7 and 199.5 K) with the CRESU method. By measuring over this temperature range and data from [8] , we have demonstrated the inversion of the branching ratio between the exothermic non-dissociative exit channel POCl 3 − and the thermo-neutral dissociative exit channel POCl 2 − + Cl. A kinetic model in terms of statistical theory is used to fit the experimental data.

The C Cl bond cleavages induced by electron attachment to 1-chloroalkyl benzenes [C 6 H 5 (CH 2 ) n Cl, n = 0, 1, 2, 3, 4] are investigated with ab initio molecular dynamics simulations. The fragment Cl − is generated and the C Cl bond cleavage time decreases with the increasing length of the alkyl chain. In the dissociative electron attachment processes, the incoming electron is initially captured to the local π* virtual orbital of the phenyl group and then transfers to the anti-bond σ* orbital of the remote C Cl moiety; the variation of the C Cl bond cleavage times shows a similar trend of the dissociation thresholds of C 6 H 5 (CH 2 ) n Cl + e − → C 6 H 5 (CH 2 ) n + Cl − .

To provide a deeper understanding of the kinetics of electron attachment to CF3, the six-dimensional potential energy surfaces of both CF3 and CF3− were developed by fitting ∼3000 ab initio points per surface at the AE-CCSD(T)-F12a/AVTZ level using the permutation invariant polynomial-neural network (PIP-NN) approach. The fitted potential energy surfaces for CF3 and CF3− had root mean square fitting errors relative to the ab initio calculations of 1.2 and 1.8 cm−1, respectively. The main active mode for the crossing between the two potential energy surfaces was identified as the umbrella bending mode of CF3 in C3v symmetry. The lowest energy crossing point is located at RCF = 1.306 A and θFCF = 113.6° with the energy of 0.051 eV above the minimum of the CF3 electronic surface. This value is only slightly larger than the experimental data 0.026 ± 0.01 eV determined by kinetic modeling of electron attachment to CF3. The small discrepancy between the theoretical and experimentally measured values is analyzed.

New flowing afterglow/Langmuir probe investigations of electronic attachment to SF6 are described. Thermal attachment rate constants are found to increase from 1.5 × 10−7 cm3 s−1 at 200 K to 2.3 × 10−7 cm3 s−1 at 300 K. Attachment rate constants over the range of 200–700 K (from the present work and the literature), together with earlier measurements of attachment cross sections, are analyzed with respect to electronic and nuclear contributions. The latter suggest that only a small nuclear barrier (of the order of 20 meV) on the way from SF6 to SF6− has to be overcome. The analysis shows that not only s-waves but also higher partial waves have to be taken into account. Likewise, finite-size effects of the neutral target contribute in a non-negligible manner.

Molecular concerted three-body dissociation is a fast process, but still can be classified into synchronous and asynchronous pathways. It is challenging in experiments to evaluate different contributions of the aforementioned mechanisms. Here, we report an experimental identification of the synchronous and asynchronous concerted three-body dissociations of temporary negative ion CH2F2− at an electron–molecule resonant state formed by electron attachment. The synchronous–asynchronous branching ratios indicate that the asynchronous process is predominant although the synchronous contribution is slightly enhanced with the increase in the electron attachment energy. This study provides two intuitive pictures of the concerted three-body dissociations, in particular for the nonequivalent-bond cleavages of a polyatomic molecule.

The rate coefficients (k’s) and the activation energies (Ea’s) of thermal electron attachment for SiCH3Cl3, SiH(CH3)2Cl, SiHCH3Cl2 and Si(C2H5)3Cl have been measured. The electron attachment processes in the chlorosilane-carbon dioxide mixtures have been investigated using a Pulsed Townsend technique in the temperature range 298 K-378 K. The increase of the rate coefficients with temperature follows the Arrhenius law and the Ea’s have been obtained from the slope of the ln(k) vs. T−1. The rate coefficients at 298 K are equal to 8.72 × 10−11cm3s−1, 6.72 × 10−11cm3s−1, 16.8 × 10−11cm3s−1 and 3.27 × 10−11cm3s−1 and activation energies are: 0.32 eV, 0.24 eV, 0.25 eV and 0.21 eV, respectively for SiCH3Cl3, SiH(CH3)2Cl, SiHCH3Cl2 and Si(C2H5)3Cl.

The present study examines the possible importance of the electron-accepting properties of odorant molecules and, in particular, the formation and decay of temporary negative ions via low-energy electron attachment, as a possible contribution towards understanding odorant recognition by olfactory receptors (OR). Fragments formed by dissociative electron attachment (DEA) of mustard oil odorants represented by a series of isothiocyanates are studied experimentally using DEA spectroscopy and DFT calculations. Relative intensities for the most abundant fragment species, S– and SCN–, are found to be characteristic for structurally similar odorants under investigation. This novel approach for the investigation of odorants may contribute to understanding the initial stages of the olfactory process and may provide a means to distinguish between odorants and their interactions with the olfactory receptor system.

Here we present a study on dissociative electron attachment (DEA) to bromotrifluoromethane, CF3Br, in the energy range from 0 to 10 eV. The dominating process observed is the formation of Br− close to 0 eV incident electron energy. The fragment ion Br− is also observed through a broad contribution from about 3 to 5 eV. In this energy range, F−, FBr− and CF2Br− are also observed, and in the Br− and F− ion yield, a weak contribution is observed close to 8.1 eV. For the DEA processes we calculate the thermochemical thresholds using conventional DFT methods, and the results are discussed in context to these, earlier work and the assignment of the underlying resonances.

We have studied low energy electron attachment to a series of alcohols with one/two chlorine atoms. We have applied two experimental methods: the electron swarm (SWARM) and negative ion mass spectrometry (NIMS). The electron attachment processes in the mixtures of chloroalcohols with carbon dioxide have been investigated using an electron swarm technique. We obtained rate coefficients ( k 's) and the activation energies ( E a 's) for CH 2 ClCH 2 OH, CH 2 ClCH 2 CH 2 OH, CH 2 ClCH(OH)CH 2 Cl, CH 2 ClCHClCH 2 OH and CH 2 ClCH(OH)CH 2 OH in the temperature range 298–378 K. The negative ion mass spectra of CH 2 ClCH 2 OH, CH 2 ClCH 2 CH 2 OH, CH 2 ClCH(OH)CH 2 Cl and CH 2 ClCH(OH)CH 2 OH has been investigated. The anion yields were measured in the electron energy range 0–15 eV.

A new approach to investigating the properties, i.e., lifetimes and decay energetics, of short-lived intermediates formed during dissociative electron attachment reactions is described that is based on measurements of the velocity and angular distributions of heavy-Rydberg ion pair states formed through electron transfer in collisions with Rydberg atoms. The experimental results are analyzed with the aid of a Monte Carlo collisions code and show that while electron capture by CF 3 I and CH 2 Br 2 leads to creation of very-short-lived intermediates capture by CCl 4 results in formation of much longer lived intermediates.

International audience; The efficient decomposition of nitroimidazoles (NIs) by low energy electrons is believed to underlie their radiosensitizing properties. Recent dissociative electron attachment (DEA) measurements showed that methylation at the N1 site unexpectedly suppresses the electron-induced reactions in 4(5)-NI. We report theoretical results that provide a clear interpretation of that astounding finding. Around 1.5 eV, DEA reactions into several fragments are initiated by a pi* resonance, not considered in previous studies. The autoionization lifetime of this anion state, which limits the predissociation dynamics, is considerably shorter in the methylated species, thereby suppressing the DEA signals. On the other hand, the lifetime of the pi* resonance located around 3 eV is less affected by methylation, which explains why DEA is still observed at these energies. Our results demonstrate how even a simple methylation can significantly modify the probabilities for DEA reactions, which may be significant for NI-based cancer therapy. Published by AIP Publishing.

Each of the three isomeric pyridyl radicals (2-, 3-, and 4-dehydropyridines) contains a lone pair and an unpaired electron. As a result, a potential two centered-three electron interaction between the radical electron and the lone pair through-space (TS) and/or through-bond (TB) can exist that may influence the stability of the radicals. Due to the change in geometrical positions relative to each other, the strength of interaction can be varied. In this study, we investigated the structural and stability aspects of pyridyl radical isomers with a major emphasis on the interaction of a nitrogen lone pair with the radical center. In order to obtain evidence for such interactions, protonated and N-oxide analogues of the corresponding isomeric pyridyl radicals have been considered in such a way to understand the consequences due to unavailability of the lone pair. Similarly, electron attachment and detachment energies at the radical center (vertical detachment energy, VDE, of corresponding anions and vertical ionization energy, VIE, of radical isomers) have been calculated to find out the interaction trend upon modification at the radical center. Different levels of theory including (U)B3LYP/cc-pVTZ, (U)M06/cc-pVTZ, CBS-QB3, single-point energy calculations at (U)CCSD(T)/cc-pVTZ, and multireference CASSCF/cc-pVTZ methods have been employed in this regard. A closer inspection of geometries, relative stability order, spin density, electrostatic potential, molecular orbitals, NBO analysis, and vibrational analysis have showed a strong and stabilizing TS interaction between the radical center and the lone pair in the case of the 2-pyridyl radical. On the other hand, the 4-pyridyl radical showed stabilizing interactions only via TB coupling, whereas the TS interaction is nonexistent. Despite the presence of both interactions in the case of the 3-pyridyl radical, their overall influence is less effective toward stability.

The knowledge of excess electron binding mechanisms in biomolecules is very important for molecular-level understanding of DNA damage by low-energy electrons. We here focus on two different excess electron binding mechanisms from the theoretical side; diffuse dipole-bound and valence-bound anionic states. We have found that long-range corrected (LC) density-functional theory (DFT) methods combined with a set of diffuse basis functions can reasonably describe electronic transformation processes between these two different anionic states. The applicability of the LC-DFT calculations is demonstrated for uracil, guanine–cytosine base pair, fructose, and uracil-iodide anion complex.

Electron transfer to pentafluorophenol and pentafluoroaniline was effected by their reaction with the metal anions Fe − , Cs − , Rb − , Ag − and Cu − , the latter formed by electrospray ionisation of solutions of the corresponding oxalate salt. Both electron transfer and dissociative electron attachment was observed. The results are compared to a recent electron attachment study to these two molecules by Omarsson et al. Based on the appearance of product ions in our study, clear differences are observed between the two methods of formation of the organic anions. Several reactions due to direct reaction with the metal anions are observed.

Relative cross sections obtained in dissociative electron attachment (DEA) reactions from crossed beams experiment are often normalised using absolute rate coefficients obtained from electron swarm experiments. Both methods, however, are carried out under rather different pressure conditions, namely single collision conditions (beam experiments) and in a higher pressure environment (electron swarm experiments). The peculiarities of the DEA process are considered with respect to these different conditions. Results from both methods are compared by means of two case studies, namely electron attachment to CF2Cl2 (swarm, effusive beam, supersonic beam containing clusters) and CClF2COOH (swarm, effusive beam).

Thermal electron attachment processes in the mixtures of CH 3 CH 2 OH, CF 3 CH 2 OH, CF 3 CF 2 CH 2 OH, (CF 3 ) 2 CHOH and CH 3 CH(OH)CF 3 with carbon dioxide have been investigated using an electron Pulsed Townsend technique. Measurements were carried out in the temperature range (298–413) K. The obtained rate coefficients depended on temperature in accordance to Arrhenius equation. From the fit to the experimental data points with function ln( k ) = ln( A )− E a / k B T the activation energies ( E a ’s) were determined. The rate coefficients at 298 K are equal to 3.2 × 10 −13 cm 3 s −1 , 5.1 × 10 −11 cm 3 s −1 , 1.1 × 10 −10 cm 3 s −1 , 3.0 × 10 −10 cm 3 s −1 and 2.6 × 10 −11 cm 3 s −1 and activation energies are: 0.37 eV, 0.25 eV, 0.28 eV, 0.20 eV and 0.23 eV, respectively for CH 3 CH 2 OH, CF 3 CH 2 OH, CF 3 CF 2 CH 2 OH, (CF 3 ) 2 CHOH and CH 3 CH(OH)CF 3 .

We study the reactivity of misonidazole with low-energy electrons in a water environment combining experiment and theoretical modelling. The environment is modelled by sequential hydration of misonidazole clusters in vacuum. The well-defined experimental conditions enable computational modeling of the observed reactions. While the NO 2 &minus, dissociative electron attachment channel is suppressed, as also observed previously for other molecules, the OH &minus, channel remains open. Such behavior is enabled by the high hydration energy of OH &minus, and ring formation in the neutral radical co-fragment. These observations help to understand the mechanism of bio-reductive drug action. Electron-induced formation of covalent bonds is then important not only for biological processes but may find applications also in technology.

Anion mass spectrometry is developed on the basis of our home-made anion velocity map imaging apparatus. The Cl− product efficiency curve for dissociative electron attachment to 1,2-dichlorobenzene is obtained from 0.2 eV to 8 eV, meanwhile the sliced images of this anion are recorded at 1.2 and 6.0 eV corresponding to two peak positions of the product efficiency curve.

A series of small carbon-doped silver clusters CAgn are studied computationally at a DFT level. Structures and stabilities are compared for a few isomers of each cluster size, with the lowest-energy systems predicted to be 3D core–shell species for n ⩾ 5. Shape alterations are tracked upon electronic excitation, ionization, and electron attachment, indicating a range from a relatively weak to a strong change. Trends in the variations of the corresponding energies, as well as in the dissociation energies for different channels, with cluster size are investigated and compared with those of pure silver counterparts. Related potential applications of such systems are discussed.