1907 ISSN 0036-0244, Russian Journal of Physical Chemistry A, 2023, Vol. 97, No. 9, pp. 1907–1913. © Pleiades Publishing, Ltd., 2023. Russian Text © The Author(s), 2023, published in Zhurnal Fizicheskoi Khimii, 2023, Vol. 97, No. 9, pp. 1254–1261. Electron Capture Dissociation by Triclocarban Molecules N. L. Asfandiarov a, *, R. G. Rakhmeev a , A. M. Safronov a , and S. A. Pshenichnyuk a a Institute of Molecular and Crystal Physics, Ufa Federal Research Center, Russian Academy of Sciences, Ufa, 450075 Russia *e-mail: nail_asf@mail.ru Received March 27, 2023; revised March 27, 2023; accepted March 30, 2023 Abstract—The formation and decay of molecular negative ions (MNIs) formed during resonant scattering of electrons by triclocarban molecules were studied by dissoiative electron attachment (DEA) spectroscopy. The most intense channel observed in the mass spectrum are MNIs formed at the thermal energy of trapped elec- trons with a lifetime relative to electron autodetachment of ~2800 μs. The experimental results were inter- preted using CAM-B3LYP/6-311+G(d,p) calculations, which made it possible to reveal a number of import- ant features of the geometry of molecular and fragment negative ions. Namely, the most stable geometry of MNIs is such that one of the chlorine atoms is coordinated with two hydrogen atoms of the structural element of urea. The charge on the chlorine atom is ~–0.7e – , which allows us to interpret this state as the result of the “roaming” of the chlorine atom in the MNI. According to calculations, the adiabatic electron affinity (EA a ) of the triclocarban molecule is 1.66 eV. Evaluation of EA a in a simple Arrhenius approximation gives 1.2– 1.4 eV. An analysis of the potential of the appearance of fragment ions with a C 6 H 3 Cl 2 NH 2 structure made it possible to discover the noncovalent structure of these pseudo-MNIs, in which the chlorine atom is coordi- nated with two hydrogen atoms of the amino group. Keywords: dissociative electron capture, long-lived molecular negative ions, electron autodetachment, triclo- carban, electron affinity, density functional theory DOI: 10.1134/S0036024423090029 Triclocarban (TCC, N-(4-chlorophenyl)-N ′-(3,4- dichlorophenyl)urea) has antibacterial and antifungal activities and has been used for a long time in hygiene and medicine. In 2017, the use of triclocarban and some other common antibacterial drugs was banned because of their questionable safety and efficiency compared to conventional soap and water; however, removing the excess amounts of these compounds from the environment still remains an important prob- lem [1]. It should be noted that one of the mechanisms of the toxic effect of halogen-substituted compounds is evidently the mechanism proposed by Gregory and associated with the formation of active dehalogenated radicals capable of initiating a chain reaction of destruction of biological membranes [2]. This mecha- nism suggests the transfer of an electron to a molecule of a toxic compound, occurring at the active site of the enzyme, which entails elimination of the halide anion from the molecular negative ion (MNI), similarly to [3], as it occurs in the gas phase in a process known as dissoiative electron attachment (DEA) [4–6]. The high selectivity of the resonance electron capture can probably explain the reasons for the difference in the action of strong electron acceptors (generally, haloge- nated environmental pollutants) on breathing and photosynthesizing organisms [7]. Thus, the study of the capture of slow (0–15 eV) electrons by triclocarban molecules is important for interdisciplinary problems. Also note that some bioremediation processes can be associated with similar elementary electron capture reactions in reductive processes [8], due to which the results may be valuable for various applications. The fundamental significance of the present study is associated with our earlier studies of the DEA of tri- closan molecules (TCS, triclosan, 5-chloro-2-(2,4- dichlorophenoxy)phenol) [9]. When electrons are captured by these molecules, long-lived (i.e., observ- able on the mass spectrometric time scale) MNIs do not form, although estimation of the adiabatic elec- tron affinity (EA a ) of the TCS molecule gives 0.92 eV. The maximum intensity is shown by the [TCS– 2(HCl)] – ions (m/z = 216) observed in the region of low electron energies in the probe beam. A peak with comparable intensity (79%) corresponds to a decay with the formation of [TCS–HCl] – ions (m/z = 252), which, in turn, decompose with release of a neutral HCl molecule according to the scheme + HCl within ~10 μs, as evidenced by the peak of meta- stable ions [10] observed at an apparent mass number m/z = 185.1 [9]. The recording of metastable anions is - + TCS e → - TCS → - - + [TCS HCl] HCl ⎯⎯→ * m - - [TCS 2HCl] STRUCTURE OF MATTER AND QUANTUM CHEMISTRY