Low-energy (0–14 eV) electron-driven processes in a racemic mixture of the chiral abscisic acid (ABA) molecules are studied using dissociative electron attachment (DEA) spectroscopy under gas-phase conditions. DFT calculations are employed to understand the electronic structure of the ABA molecule to assign the experimental findings. The lowest two normally empty π* molecular orbitals of ABA are predicted to lie in a bound region, whereas the vertical electron attachment energy to occupy the π3* LUMO+2 orbital is estimated to be 1.33 eV. The long-lived (90 μs) parent molecular negative ions are formed by thermal electron attachment via vibrational Feshbach resonance. The adiabatic electron affinity of the ABA molecule is experimentally estimated to be about 0.9 eV. With very few exceptions, the fragmentation of ABA by resonance electron attachment occurs at thermal electron energy, the dominant decay being associated with the formation of the 4-oxoisophorone negative ion (m/z = 152) and the isomeric form of the sorbic acid molecule as a neutral counterpart. The structure of ABA microbial metabolites coincides with that of the DEA products with m/z = 152, 204, and 220 and of the neutral species generated as a counterpart of the m/z = 111 negative ions. The likely relation of these findings to electron-triggered biological processes is briefly discussed in the framework of electron donation to ABA from the microbial nanowires.

The method of dissociative electron attachment (DEA) spectroscopy was used to study the attachment of electrons to 1-chloronaphthalene molecules. It has been established that the dominant channel for the decay of molecular ions is the formation of Cl- ions in three resonances at 0.7, 1.5, and 3.0 eV. Ions [M-H]- and [M-Cl]- are observed at energies from 3.5 to 8.5 eV and have two to three orders of magnitude lower formation cross sections. Long-lived molecular ions were not registered. Calculations in the DFT CAM B3LYP/6-311+G(d,p) approximation predict the presence of six stable anionic structures in which the chlorine anion is coordinated to the neutral residue via noncovalent H-Cl^--H bonds. The electron affinity of the most stable of these structures coincides with the experimentally measured value EA_a=0.2771±0.003 eV. These results agree with the previously obtained data on the DEA of molecules of bromine-substituted biphenyls, naphthalenes, and anthracenes and confirm the existence of anionic structures with non-covalent H-Hal-H bonds. Such non-covalent anion structures should be extremely reactive, which makes them promising for the synthesis of self-assembling hydrocarbon nanomembranes. Keywords: Attachment of electrons to molecules, electron affinity, potential surface, DFT calculations.

Low-energy (0-14 eV) resonance electron interaction and fragment species produced by dissociative electron attachment (DEA) for enantiomeric forms of glutamic acid (Glu) are studied under gas-phase conditions by means of DEA spectroscopy and density functional theory calculations. Contrary to a series of amino acids studied earlier employing the DEA technique, the most abundant species are not associated with the elimination of a hydrogen atom from the parent molecular negative ion. Besides this less intense closed-shell [Glu - H](-) fragment, only two mass-selected negative ions, [Glu - 19](-) and [Glu - 76](-), are detected within the same electron energy region, with the yield maximum observed at around 0.9 eV. This value matches well the energy of vertical electron attachment into the lowest normally empty pi* COOH molecular orbital of Glu located at 0.88 eV according to the present B3LYP/6-31G(d) calculations. Although the detection of asymmetric DEA properties a priori is not accessible under the present experimental conditions, "chirality non-conservation" can be associated with some decay channels. Evidently, the measured spectra for the L- and D-forms are found to be identical, the results, nevertheless, being of interest for the forthcoming experiments utilizing spin-polarized electron beam as a chiral factor in the framework of conventional DEA technique.

Electron transfer plays a crucial role in living systems, including the generation of reactive oxygen species (ROS). Oxygen acts as the terminal electron acceptor in the respiratory chains of aerobic organisms as well as in some photoinduced processes followed by the formation of ROS. This is why the participation of exogenous antioxidants in electron transfer processes in living systems is of particular interest. In the present study, using chemically induced dynamic nuclear polarization (CIDNP) and dissociative electron attachment (DEA) techniques, we have elucidated the affinity of solvated and free electrons to glycyrrhetinic acid (GA)-the aglicon of glycyrrhizin (the main active component of Licorice root). CIDNP is a powerful instrument to study the mechanisms of electron transfer reactions in solution, but the DEA technique shows its effectiveness in gas phase processes. For CIDNP experiments, the photoionization of the dianion of 5-sulfosalicylic acid (HSSA2-) was used as a model reaction of solvated electron generation. DEA experiments testify that GA molecules are even better electron acceptors than molecular oxygen, at least under gas-phase conditions. In addition, the effect of the solvent on the energetics of the reactants is discussed.

The surface topography and density of unoccupied electronic states at thermal deposition of ultrathin dibromo-bianthracene films on the ZnO surface have been studied. The electronic characteristics of unoccupied electronic states during growth of dibromo-bianthracene films to a thickness of 10 nm have been investigated by total current spectroscopy using a probe electron beam. The experimental dependences have been analyzed using theoretical calculation of the orbital energies for dibromo-bianthracene molecules by the method of density functional theory (DFT).

Приведены результаты исследования топографии поверхности и плотности незаполненных электронных состояний при термическом осаждении сверхтонких пленок дибромо-биантрацена на поверхность ZnO. Измерения электронных характеристик незаполненных электронных состояний в процессе роста пленок дибромо-биантрацена до толщины 10 нм проводили методом спектроскопии полного тока с использованием тестирующего электронного пучка. Анализ экспериментальных зависимостей проводили с использованием теоретического расчета энергий орбиталей молекул дибромо-биантрацена методом теории функционала плотности.

Acenaphtho[1,2- k ]fluoranthene ( 1 ) is synthesized via tandem cyclization during the dehydrofluorination of 1,4-di(1-naphthyl)-2,5-difluorobenzene ( 2 ) on activated γ-Al 2 O 3 . Presence of residual hydroxyl groups in alumina reduce the yield of target product 1 because of the side hydrolysis of fluoroarenes with the formation a product of partial cyclization, 9-(1-naphthyl)fluoranthen-8-ol ( 1b ). The formation of negative ions (NI) of compounds 1 and 2 in the gas phase is studied by means of dissociative electron attachment (DEA) spectroscopy. Long-lived molecular NIs 1 and 2 are registered at the thermal energies of electrons, and patterns of their fragmentation are established. The adiabatic electron affinities of compounds 1 and 2 are estimated in the Arrhenius approximation and equal 1.17 ± 0.12 and 0.71 ± 0.07 eV, respectively, which agree with data from quantum chemical modeling at the level of the density functional theory (DFT). Electronic transitions for compounds 1 and 2 are studied via optical absorption and fluorescence spectroscopy. Fluorescence quantum yields are measured, and the resulting data are interpreted according to the time dependent DFT. The electrochemical properties of compounds 1 , 1b , and 2 are studied via cyclic voltamperometry, and the levels of boundary molecular orbitals are estimated on the basis of their formal potentials of reduction and oxidation.

Low-energy (0-15 eV) resonance electron interaction with isolated tetracyanoethylene (TCNE) molecules is studied in vacuo by means of dissociative electron attachment (DEA) spectroscopy. Despite this molecule being relatively small, the long-lived molecular anions TCNE- are formed not only at thermal electron energy via a vibrational Feshbach resonance mechanism but also via shape resonances with the occupation of the π4* and π5* molecular orbitals by an incident electron. Dissociative decays of TCNE- are mostly observed at incident electron energy above the π7* temporary anion state predicted to lie at 1.69 eV by means of B3LYP/6-31G(d) calculations combined with the empirical scaling procedure. Electron attachment to the π6* orbital (predicted at 0.85 eV) leads to the generation of long-lived TCNE- species, which can decay via two competing processes: extra electron detachment, which appears in hundreds of microseconds, or elimination of two cyano groups to form the [TCNE - 2(CN)]- negative fragment on a tens of microsecond timescale. The latter is accompanied by the generation of a highly toxic cyanogen molecule as a neutral counterpart. Since the electron transfer to the acceptor molecule TCNE plays a key role in the formation of single-molecule magnets, the present data are of importance to understand the long-term behavior and likely harmful effects produced by cyanide-based prospective materials.

Electron-driven processes in isolated curcumin (CUR) molecules are studied by means of dissociative electron attachment (DEA) spectroscopy under gas-phase conditions. Elementary photostimulated reactions initiated in CUR molecules under UV irradiation are studied using the chemically induced dynamic nuclear polarization method in an acetonitrile solvent. Density functional theory is applied to elucidate the energetics of fragmentation of CUR by low-energy (0-15 eV) resonance electron attachment and to characterize various CUR radical forms. The adiabatic electron affinity of CUR molecule is experimentally estimated to be about 1 eV. An extra electron attachment to the pi(1)* LUMO and pi(2)* molecular orbitals is responsible for the most intense DEA signals observed at thermal electron energy. The most abundant long-lived (hundreds of micro- to milliseconds) molecular negative ions CUR- are detected not only at the thermal energy of incident electrons but also at 0.6 eV, which is due to the formation of the pi(3)* and pi(4)* temporary negative ion states predicted to lie around 1 eV. Proton-assisted electron transfer between CUR molecules is registered under UV irradiation. The formation of both radical-anions and radical-cations of CUR is found to be more favorable in its enol form. The present findings shed some light on the elementary processes triggered in CUR by electrons and photons and, therefore, can be useful to understand the molecular mechanisms responsible for a variety of biological effects produced by CUR.

Resonance electron attachment in a series of brominated diphenyl ethers, namely 4-bromodiphenyl ether (BDPE), 4-bromophenyl ether (BPE), and decabromodiphenyl ether (DBDE), was investigated in the gas phase by means of dissociative electron attachment spectroscopy. In addition to channels of dissociation into stable fragments, long-lived molecular negative ions with an average lifetime relative to autodetachment of the order of 60 µs were found for the last two molecules. In the case of BDPE and BPE, the most intense dissociation channel is the bromine anion, and for DBDE-the [C6Br5O]- anion. The [C6Br5O]- anion sequentially decomposes with the elimination of the bromide anion on a microsecond time scale, which is confirmed by the registration of metastable ions with an apparent mass of 12.8 a.m.u. The electron affinity of the studied molecules and the appearance energy of fragment ions were estimated with CAM-B3LYP/6-311+G(d,p).

Dissociative electron attachment (DEA) to 1-chloroanthracene and 9-chloroanthracene was investigated under gas-phase conditions. In both compounds, the elimination of the chlorine anion is the dominant channel for the dissociation of molecular negative ions (NIs). The second most intense channel leads to the formation of molecular anions (M ˉ). The autodetachment lifetime of M ˉ was measured to be about 170 & mu;s for both compounds. The widths of the M ˉ peaks indicate that molecular anions are formed via two resonances: at thermal electron energies and through a shape resonance at the energy of -0.5 eV. Adiabatic electron affinities were estimated in the framework of the simple Arrhenius model to be 0.86 eV for both molecules, the values being close to the theoretical predictions by DFT method of 0.90 eV and 0.93 eV for 1-chloroanthracene and 9-chloroanthracene respectively. Metastable negative ions are observed in the DEA spectra of both molecules, which testifies that the elimination of chlorine anions from molecular NIs appears on a time scale of several microseconds.

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 electrons with a lifetime relative to electron autodetachment of ~2800 μs. The experimental results were interpreted using CAM-B3LYP/6-311+G( d,p ) calculations, which made it possible to reveal a number of important 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 ~–0.7 e – , 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 coordinated with two hydrogen atoms of the amino group.

The method of dissociative electron attachment (DEA) spectroscopy was used to study the attachment of electrons to 1-chloronaphthalene molecules. It has been established that the dominant channel for the decay of molecular ions is the formation of Clˉ ions in three resonances at 0.7, 1.5, and 3.0 eV. Ions [M-H]ˉ and [M-Cl]ˉ are observed at energies from 3.5 to 8.5 eV and have two to three orders of magnitude lower formation cross sections. Long-lived molecular ions were not registered. Calculations in the DFT CAM B3LYP/6-311+G(d,p) approximation predict the presence of six stable anionic structures in which the chlorine anion is coordinated to the neutral residue via noncovalent H–Clˉ–H bonds. The electron affinity of the most stable of these structures coincides with the experimentally measured value EAa=0.2771±0.003 eV. These results agree with the previously obtained data on the DEA of molecules of bromine-substituted biphenyls, naphthalenes, and anthracenes and confirm the existence of anionic structures with non-covalent H–Hal–H bonds. Such non-covalent anion structures should be extremely reactive, which makes them promising for the synthesis of self-assembling hydrocarbon nanomembranes.

The results of a study of the unoccupied electronic states of ultrathin films of phenolphthalein molecules on a ZnO surface formed by atomic layer deposition technique are presented. The atomic composition of the ZnO layer was determined by X-ray photoelectron spectroscopy (XPS) and its crystallinity was characterized using X-ray diffraction. The predominance of the content of O atoms by 5-10%, compared with the content of Zn atoms, was found. The electronic characteristics of the ZnO/phenolphthalein structure were studied using total current spectroscopy (TCS) in the energy range from 5 eV to 20 eV above EF during thermal vacuum deposition of phenolphthalein films up to 8 nm thick. Phenolphthalein molecules contain two hydroxyl functional groups. The TCS results on the phenolphthalein films are compared with the TCS results obtained from films of molecules that represent the backbone of phenolphthalein molecules without hydroxyl groups. The TCS fine structure maxima of phenolphthalein films located in the energy range from 5 eV to 8 eV above EF can be associated with the boundaries of the p* bands of electronic states. The work function of the ZnO surface formed by the ALD method were 4.2±0.1 eV. The deposition of a phenolphthalein film led to a decrease in the work function of the surface by 0.1 eV.

Gas phase molecules of hexachlorobenzene (C6Cl6) were investigated by means of dissociative electron attachment spectroscopy (DEAS). Three channels of molecular negative ions decay have been identified: abstraction of Cl- and Cl-2(-) as well as electron detachment (tau(a)similar to 250 mu s at 343 K). All three channels exhibit temperature dependence. The adiabatic electron affinity estimated using a simple but typically accurate Arrhenius model (EA(a)=1.6-1.9 eV) turns out to be much higher than the quantum-chemical predictions (EA(a)=0.9-1.0 eV). We discuss the possible reasons behind the observed discrepancy.

Electron attachment to 1-chloronaphthalene molecules is studied with the aid of the dissociative electron attachment spectroscopy. It is shown that the dominant channel for the decay of molecular ions is the formation of Clˉ ions in three resonances at 0.7, 1.5, and 3.0 eV. The [M–H]ˉ and [M–Cl]ˉ ions are observed at energies from 3.5 to 8.5 eV and exhibit formation cross sections that are less by two-to-three orders of magnitude. Long-lived molecular ions are not detected. The calculations in the DFT CAM B3LYP/6-311+G(d,p) approximation predict the presence of six stable anionic structures in which the chlorine anion is coordinated with the neutral residue via noncovalent H–Clˉ–H bonds. The electron affinity of the most stable of these structures coincides with the experimental value EA a = 0.2771 ± 0.003 eV. Such results are in agreement with the existing data on the dissociative electron attachment to molecules of bromine-substituted biphenyls, naphthalenes, and anthracenes and proves the existence of anionic structures with non-covalent H–Hal–H bonds. Such non-covalent anion structures must be extremely reactive, which makes them promising for the synthesis of self-assembling hydrocarbon nanomembranes.

Four bromo-substituted derivatives of naphthalene and anthracene were studied by means of Dissociative Electron Attachment Spectroscopy. Long-lived molecular anions with lifetimes ranging from 25 to 144 mu s were observed in all molecules under investigation. In all cases molecular anion fragmentation is poor: only the Br-, [M-Br](-) and (with very small intensity) [M-H](-) species were observed, except for the case of 9,10-Br-2-anthracene. It was shown that the presence of long-lived molecular anions in 1 -Br-and 2-Br-naphthalene (tau(a)=26 mu s and tau(a)=25 mu s, respectively) does not contradict the fact that their dissociation rates measured by the pulse radiolysis method are fairly large (1.0 x10(10) s(- 1) and 1.8 x10(10) s(-1), respectively). Scanning the potential energy surface of anions in the process of positioning a bromine anion around a polarized aromatic radical revealed the presence of a series of local minima separated by potential barriers. It is inferred that the most energetically favorable structures of the 1-Br- and 2-Br-naphthalene anions should be interpreted as complexes of the bromide anion bound to the polarized aromatic radical by non-covalent Br-H bonds. Similar local minima were found in the 9 Br-and 9,10-Br-2-anthracene anions, but the energies of these structures are significantly higher than those of the "standard" anionic structures with a C-Br bond length of similar to 1.93 angstrom. The EA(a)s obtained with DFT CAM-B3LYP/6-311 +G(d,p) calculations are in acceptable agreement with the estimates made within the framework of the simple Arrhenius model from the lifetimes of molecular anions.

The results of a study of the unoccupied electronic states of ultrathin films of phenolphthalein molecules on a ZnO surface formed by atomic layer deposition technique are presented. The atomic composition of the ZnO layer was determined by X-ray photoelectron spectroscopy (XPS) and its crystallinity was characterized using X-ray diffraction. The predominance of the content of O atoms by 5-10%, compared with the content of Zn atoms, was found. The electronic characteristics of the ZnO/phenolphthalein structure were studied using total current spectroscopy (TCS) in the energy range from 5 eV to 20 eV above EF during thermal vacuum deposition of phenolphthalein films up to 8 nm thick. Phenolphthalein molecules contain two hydroxyl functional groups. The TCS results on the phenolphthalein films are compared with the TCS results obtained from films of molecules that represent the backbone of phenolphthalein molecules without hydroxyl groups. The TCS fine structure maxima of phenolphthalein films located in the energy range from 5 eV to 8 eV above EF can be associated with the boundaries of the π* bands of electronic states. The work function of the ZnO surface formed by the ALD method were 4.2±0.1 eV. The deposition of a phenolphthalein film led to a decrease in the work function of the surface by 0.1 eV. Keywords: Phenolphthalein, ultrathin films, ZnO, atomic layer deposition, electronic properties, low-energy electron spectroscopy, X-ray diffraction, X-ray photoelectron spectroscopy.

The processes of formation and decay of negative molecular ions (NMI) of p-fluoranil [2,3,5,6-tetrafluoro-1,4-benzoquinone (FA)] and p-chloranil [2,3,5,6-tetrachloro-1,4-benzoquinone (CA)] in the gas phase were investigated. In both cases, long-lived NMIs were found in two resonances, at thermal electron energies and in the region of 0.8-0.9 eV, with lifetimes relative to electron ejection of τa ∼ 600 µs. The dissociation of molecular NIs with the formation of fragment ions [M-COF2]-, [M-CO]-, and Cl- proceeds at microsecond times, which is confirmed by the registration of the corresponding metastable ions. It is shown that the dependence of the lifetime of MNIs on the electron energy can be explained by the presence of a transition state at an energy of ∼0.5 eV.