RESUMEN
Benzonitrile (BZN) and carbon tetrachloride (CCl4) are versatile solvents used as a precursor for the synthesis of many products. As multi-usage molecules, these compounds may be involved in sustainable chemistry processes such as the cold plasma techniques for which the generated electrons are known to be responsible for reactions. Therefore, it is desirable to explore the interaction of low energy electrons with the co-compounds in the gas phase. The production of chlorine and cyanine anions, initiated by the electron collision with CCl4 and BZN, respectively, undergo nucleophilic substitution SN2 reaction with the precursors molecules for the synthesis of chlorobenzene and tricholoacetonitrile. The mechanism of fragmentation of benzonitrile and the synthesis reactions are rationalized by DFT calculations. The yield of the cyanine anion produced from the ion reaction increases with the temperature of the admixture gas, probed in the 25-100 °C temperature range. The present work may contribute to a potential process for the production of chlorobenzene for instance via (cold) plasma techniques.
RESUMEN
Weakly bound non-valence anions are molecular systems where the excess electron stabilizes in a very diffuse orbital whose size, shape, and binding energy (â¼1-100 meV) are governed by the long-range electrostatic potential of the molecule. Its binding energy comes mainly from charge-dipole or charge-multipole interactions or dispersion forces. While highly correlated methods, like coupled cluster methods, are considered to be the state of the art for describing anionic systems, especially when the electron lies in a very diffuse orbital, we consider here the possibility to use DFT-based calculations. In such molecular anions, the outer electron experiences long-range exchange and correlation interactions. We show that DFT can describe long-range bound states provided that a correct asymptotic exchange and correlation potential is used, namely, that from a range-separated hybrid functional. This opens an alternative to the computationally demanding highly correlated method calculations. It is also suggested that the study of weakly bound anions could help in the construction of new DFT potentials to study systems where nonlocal effects are significant.
RESUMEN
The interaction of low-energy electron collisions with molecules may lead to temporary anions via resonant processes. While experimental measurements, e.g., electron transmission spectroscopy or dissociation electron attachment spectroscopy, are efficient to characterize the temporary anions, simulating the electron attachment is still very challenging. Here, we propose a methodology to calculate the resonance energies of the electron attachment using ab initio (TD)-DFT calculations together with two different basis sets: a large basis set with diffuse functions to compute the vertical electron affinity and a smaller one to calculate the excitation energy of the anion. To demonstrate the capabilities and the reliability of this computational approach, 53 resonance energies from 18 molecules are calculated and compared to experimental data.
RESUMEN
In this contribution the dissociative electron attachment to metabolites found in aerobic organisms, namely oxaloacetic and citric acids, was studied both experimentally by means of a crossed-beam setup and theoretically through density functional theory calculations. Prominent negative ion resonances from both compounds are observed peaking below 0.5 eV resulting in intense formation of fragment anions associated with a decomposition of the carboxyl groups. In addition, resonances at higher energies (3-9 eV) are observed exclusively from the decomposition of the oxaloacetic acid. These fragments are generated with considerably smaller intensities. The striking findings of our calculations indicate the different mechanism by which the near 0 eV electron is trapped by the precursor molecule to form the transitory negative ion prior to dissociation. For the oxaloacetic acid, the transitory anion arises from the capture of the electron directly into some valence states, while, for the citric acid, dipole- or multipole-bound states mediate the transition into the valence states. What is also of high importance is that both compounds while undergoing DEA reactions generate highly reactive neutral species that can lead to severe cell damage in a biological environment.