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The molecules of 2-methylquinoxalin and 2,3-dimethylquinoxalin were studied by mass spectrometry of negative ions of resonant capture of slow (0-15 eV) electrons. These compounds have antimicrobial, antifungal, bactericidal and preservative properties, and are widely used in medicine and the food industry. The average lifetime of molecular negative ions (NI)relative to electron auto-cleavage is measured experimentally. The most probable structures of fragment ions ([M – H]–, formed during the decay of molecular NI, are revealed. Within the framework of the Arrhenius approximation, the value of the adiabatic electron affinity (EAa) was estimated. It is found that the theoretical values of EAa calculated by the B3LYP/6-31+G(d) method with minimal addition of diffuse functions as the difference between the total energies of the neutral molecule and the radical anion correlate with the values of EAa obtained from the experiment.

Resonance attachment of low-energy (0–15 eV) electrons to molecules of 4.7- and 6.7-dihydroxycoumarin was investigated by means of negative ion mass spectrometry. These natural compounds possess biological activity associated with antioxidant and bactericidal properties. The most probable structures of the fragment negative ions ([M – H]–, [M – 2H]–, [M – СО]–, [M – СОH]–, [M – СООH]– etc.) were predicted by means of analysis of decay channels for the molecular negative ions using the results of density functional theory calculations. Mean lifetime for molecular negative ions of 4.7-dihydroxycoumarin relative to electron autodetachment was measured. The adiabatic electron affinity (EAa) was estimated in the framework of the Arrhenius approximation. It was found that EAa values calculated at B3LYP/6-31+G(d) level with minimal addition of diffuse functions as a difference between the total energies of a neutral molecule and its radical anion correlate with experimental EAa values.

Low-energy (0-15 eV) electron interactions with gas-phase 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane (F4-TCNQ) molecules are studied under single collision conditions using dissociative electron attachment (DEA) spectroscopy. The experimental findings are supported by density functional theory calculations of the virtual orbital energies and energetics of the dissociative decays. Long-lived molecular negative ions F4-TCNQ– are detected in a wide electron energy range (0-3 eV) with electron detachment times in the range of milliseconds. Although plenty of decay channels are observed, their intensities are found to be very small (two to four orders of magnitude relative to the F4-TCNQ– signal). These findings prove that the structure of this strong electron-accepting molecule bearing an excess electron is robust in its electronic ground state, even when highly (up to 6 eV) vibrationally excited. As many as nine metastable fragment anions formed slowly (in the 16-23 µs range) are found in the negative ion mass spectrum of F4-TCNQ, as never observed before in compounds possessing high electron-accepting ability. The present results shed some light on microsecond dynamics of isolated F4-TCNQ molecules under conditions of excess negative charge, which are important for understanding the functionality of nanoscale devices containing this molecule as a structural element.

Electron-driven processes in the triclosan molecule are studied under gas-phase conditions using dissociative electron attachment (DEA) spectroscopy with the support of density functional theory calculations. Several decay channels of the short-lived (less than 17 µs) molecular anion of triclosan are associated with excitation of internal rotations of the phenyl rings around the C–O bonds. This leads to production of a dioxin anion, by elimination of a neutral HCl molecule, or negatively charged hypochlorous acid and dibenzofuran as neutral counterpart. These decays are accompanied by cleavage and formation of several covalent bonds and appear on the microsecond timescale, as confirmed by detection of metastable anions. On the basis of the present and earlier findings, DEA spectroscopy demonstrates to be a suitable technique for studying internal rotations in negative ions, although quite different from the experimental techniques – microwave and Raman spectroscopies – usually employed to study internal rotations in neutral molecules.

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.