Electron Attachment Processes Research Articles

Theoretical Study on the Dissociation Mechanism of Thiophene in the UV Photoabsorption, Ionization, and Electron Attachment Processes

ABSTRACTA computational study on the intricate mechanism of thiophene ring‐fragmentation (TRF) in the UV photodissociation, dissociative ionization, and dissociative electron attachment process has been performed. The complete fragmentation process is studied using high level G4 composite method for neutral, cationic, and anionic species by elucidating a detailed mechanism for various reaction channels. The study shows that for neutral thiophene, the major pathway is the migration of H atom and subsequent fragmentation through a transition state yielding acetylene (HC≡CH) and H2C=C=S. However, for the thiophene cation, the acetylene (HC≡CH)+H2C=C=S+ channel is a two‐step and barrier less process. The onset of CH3+HC=C=C=S channel has been observed in both the thiophene cation and anion which was absent in the neutral analogue. Similarly, the onset of H2S+HC≡C—C≡CH channel has been found to operate only in the thiophene cation. Others, such as HCS and HS elimination channels have been found in all the species showing similar dissociation mechanism. For the thiophene anion, the TRF process is very much similar to that of thiophene cation. However, the reaction enthalpies of the various elimination channels in the anionic species are lower as compared to that of cationic species. During the study, the ionization energies and electron affinities of various molecules/radicals produced during the fragmentation process of thiophene were also computed.

Dosimetric saturation effect study and correction calculation method of ionization chamber at ultra-high dose rate (FLASH)

Backgroundand Purpose: FLASH radiotherapy has aroused strong interest among researchers, but how to monitor dose in real time and lack of generally accepted ion correction model are one of the challenges. This study is based on previous research work, the dosimetric verification of FLASH ionization chamber was performed using a 200 keV electron beam irradiation platform at an ultra-high dose rate. At the same time, the finite element program is written to analyze and calculate the ion correction factor. In addition, the results are compared with the calculation results of Boag model. MethodsIn this study, the pressure of the sensitive volume in the detector was adjusted to 16 mbar for the purpose of dosimetry of dose rates in excess of 100 Gy/s. In order to monitor the response of the detector, the beam frequency and pulse width were adjusted accordingly. However, due to the saturation effect of the ionization chamber, the processes of electron ion pair drift, attachment, recombination and diffusion in the sensitive volume were modelled on the basis of the relevant physical principles. Finally, the correction factor was calculated by the finite element analysis. ResultsThe experimental results demonstrate that the FLASH ionization chamber is capable of meeting the requirements of dose measurement and beam monitoring of the electron beam at ultra-high dose rates. Furthermore, the analytical model is able to more accurately describe the saturation effect and calculate the correction factor. ConclusionIn this paper, the method of reducing air pressure is employed for the purpose of monitoring the dose of ultra-high dose rate. Simultaneously, the finite element method was employed to analyze the physical process of electron–ion pairs within the chamber and to calculate the ion correction factor analytically. A comparison with the Boag model indicates that the proposed approach is effective. However, the results exhibit a certain degree of divergence from experimental outcomes. This discrepancy may be attributed to the influence of the input parameters, which require further calibration to enhance the accuracy and the robustness of the model.

Fourth-Order Algebraic Diagrammatic Construction for Electron Detachment and Attachment: The IP- and EA-ADC(4) Methods.

We present a non-Dyson fourth-order algebraic diagrammatic construction formulation of the electron propagator, featuring the distinct IP- and EA-ADC(4) schemes for the treatment of ionization and electron attachment processes. The algebraic expressions have been derived automatically using the intermediate state representation approach and implemented in the Q-Chem quantum-chemical program package. The performance of the novel methods is assessed with respect to high-level reference data for ionization potentials and electron affinities of closed- and open-shell systems. While only minor improvements over the corresponding third-order methods are observed for one-hole ionization and one-particle electron attachment processes from closed-shell systems (MAEIP-ADC(4) = 0.27 eV and MAEEA-ADC(4) = 0.05 eV), a significantly enhanced performance is found in case of open-shell reference states (MAEIP-ADC(4) = 0.11 eV and MAEEA-ADC(4) = 0.02 eV). A particularly appealing feature of the novel methods is their accurate treatment of satellite transitions. For closed-shell reference states, we obtain accuracies of MAEIP-ADC(4) = 0.81 eV and MAEEA-ADC(4) = 0.27 eV, while in case of open-shell reference states, mean absolute errors of MAEIP-ADC(4) = 0.15 eV and MAEEA-ADC(4) = 0.27 eV are found.

An Innovative Approach for Precise Identification of the Lowest Unoccupied Molecular Orbital Using the Parametric Equation of Motion.

The lowest unoccupied molecular orbital (LUMO) plays a crucial role in quantum chemistry, but current quantum chemistry calculations fail to provide useful virtual orbitals, making it challenging to explore various processes such as photochemical reactions, electron attachment, reduction, or excitation processes. The LUMO obtained from the self-consistent field (SCF) solution can not be relied upon and needs to be identified as they are often present among the continuum states having almost similar energies. The nuclear charge stabilization method has been proven useful in identifying LUMO. Herein, we have proposed the application of parametric equations of motion (PEM) in conjunction with nuclear charge stabilization method to identify the LUMO obtained from the SCF solution exhibiting stability with different basis sets including diffuse functions.

Novel Approach for Predicting Vertical Electron Attachment Energies in Bulk-Solvated Molecules.

When low-energy electrons interact with molecules, they can give rise to transient anion states commonly known as resonances. These states are formed through vertical electron attachment processes and have the potential to induce various forms of DNA lesions, including base damage, single- and double-strand breaks, cross-links, and clustered lesions that are challenging to repair. So far, most experimental and theoretical studies have investigated the formation of resonances of (bio)molecules in the gas phase or in microsolvated environments. Since cellular environments are mainly composed of water molecules, it is crucial to understand how bulk water affects the resonances of (bio)molecules. Given the existing gap in studies on resonances of bulk-solvated molecules, we propose a novel theoretical-computational approach to address this void. Our approach combines the multibasis-set (time-dependent-)density functional theory and self-consistent sequential quantum mechanics/molecular mechanics polarizable electrostatic embedding methods. We apply this combined methodology to predict the vertical electron attachment energies of 1-methyl-5-nitroimidazole (1M5NI), a well-known radiosensitizer model, in bulk water. In addition, we analyze the rapid mutual polarization between the resonances (both shape- and core-excited) of 1M5NI and the surrounding bulk water environment. For comparison, we also studied the isolated and microsolvated 1M5NI. Overall, while the polarization of the environment is clearly sensitive to the solute charge, causing a significant impact on the vertical electron affinity and consequently on the attachment electron energies, it does not have a significant impact on the excitation energies of the anion.

Dissociative properties of C4F6 obtained using computational chemistry

The electronic properties of C4F6 were investigated by using computational chemistry to clarify the dissociative channels in the process plasma. The results show the mainly ionized ion is C3F3 + (CF2=C=CF+; propargyl ion) which is observed in the mass spectrum with the electron energy of 70 eV, and the intermediate molecular structure to produce C3F3 + ion is methyl allene ion (CF2=C=CF–CF3 +). The molecular ion C4F6 + is also mainly produced in the ionization threshold region. For the excited states, the calculated results suggest that CF2CFCF + CF2 dissociation takes place in the energy region higher than 7.0 eV and C2F3 + C2F3 dissociation takes place in the energy region higher than 8.0 eV. In the electron attachment process, the vertical electron attachment energy was calculated as 1.1 eV and the nonadiabatic negative ion energy was −0.2 eV lower than the energy of neutral C4F6.

Observation of Renner-Teller and predissociation coupled vibronic intensity borrowing in dissociative electron attachment to OCS.

We use a time-of-flight-based velocity map imaging method to look into the dissociative electron attachment to a linear OCS molecule at electron beam energies ranging from 4.5 to 8.5eV. The conical time-gated wedge slice imaging method is utilized to extract fragments' slice images, kinetic energy (KE), and angular distributions, which provide a complete kinematic understanding of this experiment on the dissociative electron attachment process. We observe that the formation of S- is relatively higher than the O- product. Three distinct dissociative KE bands of S-/OCS have been observed for the 5.0 and 6.5eV resonance positions. We notice a prominent rovibrationally coupled bimodality for each KE band in the variation of the most probable KE values. When the electron energy is changed from 5.5 to 6.0eV, we observed vibronic intensity borrowing in the highest momentum band of S- via the Σ → Π symmetric dipole-forbidden transitions within the 1.5eV energy gap. Multiple peaks in the angular distributions of S- and their modeling indicate the presence of Renner-Teller vibronic splitting. Using Q-Chem's implemented complex absorbing potential-equation of motion-electron affinity coupled cluster singles and doubles aug-cc-pVDZ+4s3p level of multireference-based electronic structure theory, we confirm the presence of OCS temporary negative ion bending vibrations and Renner-Teller vibronic splittings for the Π symmetric states. Additionally, we notice the presence of a non-radiative predissociation continuum (bringing down the rotational spectrum) and speed-dependent angular anisotropy in the S- fragmentation. Our findings at the resonance of OCS at 6.5eV closely align with the prediction of vibronic intensity borrowing by Orlandi and Siebrand [J. Chem. Phys. 58, 4513 (1973)].

Theoretical Investigation on excited dipole bound states of alkali-containing diatomic anions

Abstract Information about electronic excited states of molecular anions plays an important role in investigating the electron attachment and detachment processes. Here we present a high-level theoretical study on the electronic structures of twelve alkali-metal-containing diatomic anions MX- (MX = LiH, LiF, LiCl, NaF, NaCl, NaBr, RbCl, KCl, KBr, RbI, KI, and CsI). The equation-of-motion electron-attachment coupled-cluster singles and doubles (EOM-EA-CCSD) method is carried out to calculate the electron binding energies (EBEs) of 10 electronic excited states of each of the twelve molecule anions. With addition of different s-/p-/d- diffusion functions in the basis set, we have identified possible excited dipole bound states (DBSs) of each anion. With the investigation of EBEs on the twelve MXs with dipole moment (DM) up to 12.1 D, we evaluate the dependence of the number of anionic excited DBSs on molecular DM. The results indicate that, there exists at least two or three DBSs of anions with the molecular DM larger than 7 D and a molecule with DM > 10 D can sustain a π-DBS of the anion. Our study would shed some implications on the excited DBSs electronic states of alkali-metal-containing diatomic molecules.

New emission band of solid nitrogen

New results on the study of radiation effects in solid nitrogen and N2-doped Ne matrix are presented, with a focus on the so-called γ-line origin. The irradiation was carried out in dc regime with an electron beam of subthreshold energy. The relaxation dynamics was monitored by emission spectroscopy: cathodoluminescence (CL) and nonstationary luminescence (NsL), along with current activation spectroscopy. Thermally stimulated luminescence (TSL) and exoelectron emission (TSEE) of pure nitrogen and N2 in the Ne matrix were measured in a correlated manner. Three emission bands were recorded in the NIR CL spectra of solid N2: 794, 802, and 810 nm. The band at 810 nm was detected for the first time. These three bands are characterized by similar behavior and form molecular series with spacing between adjacent vibrational energy levels of the ground state of 125 and 123 cm−1. These data cast doubt on the recently made assumption that the γ-line is attributed to the emission of the nitrogen anion N− [R. E. Boltnev, I. B. Bykhalo, I. N. Krushinskaya et al. Phys. Chem. Chem. Phys. 18, 16013 (2016)]. The processes of electron attachment and neutralization of positively charged species are discussed. It has been established that the γ-line in the TSL spectra of pure nitrogen and N2-doped Ne matrix correlates with TSEE currents and recombination emission of O+, N2+, and N4+ ions, which indicates its connection with the neutralization reaction. The measurement of NsL supported this conclusion. A new possible assignment of the γ-line and its satellites to the emission of tetranitrogen N4 is discussed.

Mechanistic insights into the electron attachment process to guanosine in the presence of arginine.

The attachment of low-energy electrons (LEEs) to DNA biomolecules leads to irreversible damage. However, the behavior of this interaction can be influenced by the presence of amino acids. Herein, we have delved into the mechanism of electron attachment to the guanosine in the presence of arginine. This study used combined molecular dynamics (MD) simulations and quantum mechanics/molecular mechanics (QM/MM) approaches to collect and optimize the geometries having hydrogen-bonds (H-bonds) between guanosine and arginine, respectively, followed by atom centered density matrix propagation (ADMP) simulations to assess the electron attachment ability of guanine with and without arginine. The vertical detachment energy (VDE) and natural population analysis (NPA) suggest that the electron attached to guanosine occurs more readily due to the H-bonds between guanosine and arginine. The singly occupied molecular orbitals (SOMOs), VDE, and NPA from ADMP results corroborated the idea that in the presence of arginine, the electron effectively attached to the guanosine moiety while the auto detachment process becomes less probable in the case of arg-guanosine (two-H bonds). However, in the presence of arginine, the dissociative electron attachment (DEA) process for guanosine is exothermic, while in the absence of arginine, it is endothermic. This study provides new insight into the process of radiation damaging biological systems by elucidating the DEA to DNA subunits in the presence of amino acids, paving the way for a deeper understanding of radiation-induced damage in biological systems.

<i>Ab initio</i> molecular dynamics study on dissociation process of 2-thiouracil and its tautomers under low-energy electron interactions

When biomolecules interact with high-energy particles and rays, they are directly ionized or dissociated, then a large number of low-energy electrons are formed as secondary particles. These low-energy electrons will attach to biomolecules, and trigger off the secondary dissociation, forming free radicals and ions with high reactivity, which can damage the structure and function of the biomolecule and cause irreversible radiation damage to the biomolecule. It is important to study the low-energy dissociative electron attachment (DEA) process of biomolecules for understanding radiation damage to biological organisms. Currently, the theoretical studies of DEA have mainly focused on the bound states of negative ions and the types of resonances in the dissociation process. The dissociation process is well described by quantum computational method, but the diversity and complexity of dissociation channels present in the dissociation process of 2-thiouracil molecule also pose a great computational challenge to these methods. In addition, the quantum computational methods are not ideal for dealing with the discrete states of chemical bonds and the problem of continuity coupling of electrons. The dissociation dynamics of biomolecules mainly results from ionization and electron attachment. <i>Ab initio</i> molecular dynamics simulation can reasonably describe these processes. In light of these considerations, <i>ab initio</i> molecular dynamics simulation is used in this work to study dynamic variation process in DEA. The low-energy electron dissociative attachment to 2-thiouracil in the gas phase is studied by using the Born-Oppenheimer molecular dynamics model combined with density functional theory. It is found that an important dehydrogenation phenomenon of 2-thiouracil and its tautomers occurs in the DEA process, and that the N—H and C—H bond are broken at specific locations. Due to the loss of hydrogen atoms at the N and C sites, the closed-shell dehydrogenated negative ion (TU-H)<sup>–</sup> forms, which is the most important negative ion fragments in the dissociation process. The potential energy curves, the bond dissociation energy and the electron affinity energy of the broken bond show that the N—H bond is the most likely to break, indicating the formation of the negative ion (TU-H)<sup>–</sup> mainly comes from the breaking of N—H bond. The theoretical calculations in this work are in good agreement with the available experimental results, indicating that the chosen calculation method is fully reliable. ​The BOMD simulations can not only dynamically recover the process of dissociative attachment of low-energy electrons to 2-thiouracil, but also more importantly provide an insight into the mechanisms of dehydrogenation and dissociation channels of 2-thiouracil molecules in DEA process.

New approach to instantaneous polarizable electrostatic embedding of the solvent

The sequential quantum mechanics/molecular mechanics (S-QM/MM) method efficiently computes solvent effects on the electronic properties of solutes. The protocol involves two steps: solute-solvent configurations are generated from MM simulations, while the solute properties are computed in the subsequent QM step. A well-known difficulty within the S-QM/MM framework is the description of the polarization of the MM partition (electrostatic embedding) in case the electronic structure of the solute undergoes sudden changes, such as in electronic excitation, electron attachment or detachment processes. To improve the description of the electronic polarization of the solvent, we propose the self-consistent S-QM/MM polarizable electrostatic embedding (scPEE-S-QM/MM) method, which generates individual atomic charges for the solvent molecules due to solute-solvent and solvent-solvent polarization. The electronic properties calculated for the neutral and anion states of 1-methyl-4-nitroimidazole were found to be significantly affected by solvent polarized electrostatic embeddings obtained for different solute electronic states. Finally, the method also provides accurate results for bulk water.

The performance of approximate equation of motion coupled cluster for valence and core states of heavy element systems

The equation of motion coupled cluster singles and doubles model (EOM-CCSD) is an accurate, black-box correlated electronic structure approach to investigate electronically excited states and electron attachment or detachment processes. It has also served as a basis for developing less computationally expensive approximate models such as partitioned EOM-CCSD (P-EOM-CCSD), the second-order many-body perturbation theory EOM (EOM-MBPT(2)) and their combination (P-EOM-MBPT(2)) [S. Gwaltney et al., Chem. Phys. Lett. 248, 189–198 (1996)]. In this work we outline an implementation of these approximations for four-component based Hamiltonians and investigate their accuracy relative to EOM-CCSD for valence excitations, valence and core ionisations and electron attachment, and this for a number of systems of atmospheric or astrophysical interest containing elements across the periodic table. We have found that across the different systems and electronic states of different nature considered, partition EOM-CCSD yields results with the largest deviations from the reference, whereas second-order based approaches tend show a generally better agreement with EOM-CCSD. We trace this behaviour to the imbalance brought about by the removal of excited state relaxation in the partition approaches, with respect to degree of electron correlation recovered.

Algebraic Diagrammatic Construction Schemes Employing the Intermediate State Formalism: Theory, Capabilities, and Interpretation.

Algebraic diagrammatic construction (ADC) schemes represent a family of ab initio methods for the calculation of excited electronic states and electron-detached and -attached states. All ADC methods have been demonstrated to possess great potential for molecular applications, e.g., for the calculation of absorption or photoelectron spectra or electron attachment processes. ADC originates from Green's function or propagator theory; however, most recent ADC developments heavily rely on the intermediate state representation or effective Liouvillian formalisms, which comprise new ADC methods and computational schemes for high-order properties. The different approaches for the calculation of excitation energies, ionization potentials, and electron affinities are intimately related, and they provide a coherent description of these quantities at equivalent levels of theory and with comparable errors. Most quantum chemical program packages contain ADC methods; however, the most complete ADC suite of methods can be found in the recent release of Q-Chem.

Resonance Electron Capture by 5-Methyluridine and 3'-Deoxythymidine Molecules

Negative ion mass spectrometry is used to study processes of resonant electron attachment by 5‑methyluridine and 3'-deoxythymidine nucleoside molecules in the electron 0–14 eV range of energies. It is established that they are similar to those in nucleosides studied earlier (uridine, deoxyuridine, thymidine). The main channels of the fragmentation of molecular ions are revealed, and the absolute cross sections for the formation of fragment ions are determined. It is found that the intensity of the breaking the glycosidic bond in 3'-deoxythymidine in the region of low energies is two and a half orders of magnitude below the one in stavudine, testifying to the prospect of replacing the antiretroviral drug stavudine with 3'-deoxythymidine if radiation therapy is required for oncological diseases contracted as complications of HIV.

Water-assisted electron capture exceeds photorecombination in biological conditions.

A decade ago, an electron-attachment process called interatomic Coulombic electron capture has been predicted to be possible through energy transfer to a nearby neighbor. It has been estimated to be competitive with environment-independent photorecombination, but its general relevance has yet to be established. Here, we evaluate the capability of alkali and alkaline earth metal cations to capture a free electron by assistance from a nearby water molecule. We introduce a characteristic distance rIC for this energy transfer mechanism in equivalence to the Förster radius. Our results show that water-assisted electron capture dominates over photorecombination beyond the second hydration shell of each cation for electron energies above a threshold. The assisted capture reaches distances equivalent to a fifth to seventh solvation shell for the studied cations. The far reach of the assisted electron capture is of significant general interest to the broad spectrum of research fields dealing with low-energy electrons, in particular radiation-induced damage of biomolecules. The here introduced distance measure will enable quantification of the role of the environment for assisted electron attachment.

Dissociation channels of c-C4F8 to C2F4 in reactive plasma

Progress in computational methods and personal computing has made possible more accurate estimations for primary dissociation channels and energies. The main dissociation route is revealed to be via the 7E excited state with an energy of 12.23 eV, which is composed of transitions from the highest occupied molecular orbital with b1 symmetry to some degenerate unoccupied e molecular orbitals. The main contributing e orbitals consisted of antibonding combination of C2F4 π-bonding orbitals. This degenerate 7E state is lowered by non-adiabatic transitions through the conical interactions on the dissociating route to 2C2F4, so the energy is finally relaxed at the dissociative second lowest 1E excited state leading to 2C2F4 production. In the electron attachment process, the calculated results show that the F− ion is produced from the excited states of the D4h c-C4F8 − ion through conical interactions at the energies of 4.3 eV, 5.6 eV, and 5.0 eV, along the C–F dissociation route.

Electron and Positron Scattering Cross Sections from CO2: A Comparative Study over a Broad Energy Range (0.1-5000 eV).

In this Review, we present a comparative study between electron and positron scattering cross sections from CO2 molecules over a broad impact energy range (0.1–5000 eV). For electron scattering, new total electron scattering cross sections (e-TCS) have been measured with a high resolution magnetically confined electron beam transmission system from 1 to 200 eV. Dissociative electron attachment processes for electron energies from 3 to 52 eV have been analyzed by measuring the relative O– anion production yield. In addition, elastic, inelastic, and total scattering cross section calculations have been carried out in the framework of the Independent Atom Model by using the Screening Corrected Additive Rule, including interference effects (IAM-SCARI). Based on the previous cross section compilation from Itikawa (J. Phys. Chem. Ref. Data, 2002, 31, 749−767) and the present measurements and calculations, an updated recommended e-TCS data set has been used as reference values to obtain a self-consistent integral cross section data set for the elastic and inelastic (vibrational excitation, electronic excitation, and ionization) scattering channels. A similar calculation has been carried out for positrons, which shows important differences between the electron scattering behavior: e.g., more relevance of the target polarization at the lower energies, more efficient excitation of the target at intermediate energies, but a lower total scattering cross section for increasing energies, even at 5000 eV. This result does not agree with the charge independence of the scattering cross section predicted by the first Born approximation (FBA). However, we have shown that the inelastic channels follow the FBA’s predictions for energies above 500 eV while the elastic part, due to the different signs of the scattering potential constituent terms, remains lower for positrons even at the maximum impact energy considered here (5000 eV). As in the case of electrons, a self-consistent set of integral positron scattering cross sections, including elastic and inelastic (vibrational excitation, electronic excitation, positronium formation, and ionization) channels is provided. Again, to derive these data, positron scattering total cross sections based on a previous compilation from Brunger et al. (J. Phys. Chem. Ref. Data, 2017, 46, 023102) and the present calculation have been used as reference values. Data for the main inelastic channels, i.e. direct ionization and positronium formation, derived with this procedure, show excellent agreement with the experimental results available in the literature. Inconsistencies found between different model potential calculations, both for the elastic and inelastic collision processes, suggest that new calculations using more sophisticated methods are required.

Structural, spectroscopic and electron collisional studies of isoxazole (C3H3NO)

• Comprehensive structural, spectroscopic and electron collision data of Isoxazole. • DFT calculations of ground state geometry and vibrational frequencies. • Comparison with earlier data; confirmation/revision of vibronic assignments. • Vertical excitation energies for singlet and triplet states using TDDFT. • Low energy electron scattering data for Isoxazole from 0.1-20 eV. The structural, spectroscopic, and electron collision data of Isoxazole (C 3 H 3 NO) were subjected to extensive computational studies. Spectroscopic calculations were performed on ground and excited states using the density functional theory (DFT) and the time dependent density functional theory (TDDFT) respectively. Ground state geometry and vibrational frequencies agree well with earlier works and lead to re-assignment of a few vibrational bands. Theoretically predicted singlet and triplet excitation energies are in good agreement with earlier experimental data, while predicted oscillator strengths of singlet states correlate well with the observed relative spectral intensities. The electron collision data for isoxazole molecule were calculated using Quantemol-N, which employs the UK Molecular R-matrix codes. These calculations were performed for the total elastic cross-sections along with their symmetrical components, differential and momentum transfer cross-sections, inelastic scattering cross-sections comprising of discrete electronic excitation, ionization and dissociative electron attachment processes. We employed the two most popular theoretical approaches to calculate the electron impact ionization cross-sections viz. Complex scattering potential-ionization contribution (CSP-ic) and the Binary encounter Bethe (BEB) model. The rate coefficients for elastic and inelastic processes were estimated over a wide electron temperature range. In addition to scattering calculations, the other motivation was to obtain resonances which are signatures of many significant low energy phenomena. The first two peak correspond to π* shape resonances which are observed at 2.1 eV and 4.69 eV and are in accordance with the earlier reported data. The third peak is observed at 10.96 eV which may be attributed to the σ* shape resonance.

A Missing Puzzle in Dissociative Electron Attachment to Biomolecules: The Detection of Radicals

Ionizing radiation releases a flood of low-energy electrons that often causes the fragmentation of the molecular species it encounters. Special attention has been paid to the electrons’ contribution to DNA damage via the dissociative electron attachment (DEA) process. Although numerous research groups worldwide have probed these processes in the past, and many significant achievements have been made, some technical challenges have hindered researchers from obtaining a complete picture of DEA. Therefore, this research perspective calls urgently for the implementation of advanced techniques to identify non-charged radicals that form from such a decomposition of gas-phase molecules. Having well-described DEA products offers a promise to benefit society by straddling the boundary between physics, chemistry, and biology, and it brings the tools of atomic and molecular physics to bear on relevant issues of radiation research and medicine.