Galeev, Rustem V

Faizullin M.G., Galeev R.V.

Microwave spectroscopy is used to study the microwave rotational spectrum of a 2-methyltetrahydrofuran molecule in three excited states of hindered pseudorotation. The rotational constants and components of the molecule’s dipole moment in these states are determined. An attempt is made to determine the shape of the potential curve of the molecule’s hindered pseudorotation, based on these data and the results from quantum-chemical calculations.

Asfandiarov N.L., Galeev R.V., Pshenichnyuk S.A.

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 τ a ∼ 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.

Tayupov M., Markova A., Safronov A., Galeev R.

The method of negative ion mass spectrometry of resonant attachment of low energy electrons (0-15 eV) was used to identify and determine the type of impurities in the studied samples of benzofuran-3(2H)-one and benzofuran-2(3H)-one. An analysis of the decay channels of molecular negative ions (NIs) into stable fragments using the results of quantum-chemical calculations in the approximation of the density functional theory made it possible to determine the most probable structures of impurity molecules, as well as fragment ions ([M - H]-, [M - 2H]-, [M - СО]-).

Asfandiarov N.L., Muftakhov M.V., Safronov A.M., Galeev R.V., Pshenichnyuk S.A.

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 EAa = 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.

Faizullin M.G., Galeev R.V.

A microwave spectroscopic study is performed of the rotational spectrum of the 2-methyl-1,3-dioxolane molecule in states $${v}$$ = 7–9 of hindered pseudorotation. The rotational constants of the molecules in these states are determined. An attempt is made to clarify the shape of the potential curve of hindered pseudorotation of the molecule, based on the authors’ findings and data determined earlier for states $${v}$$ = 0–6.

Pshenichnyuk S.A., Modelli A., Vorob’ev A.S., Asfandiarov N.L., Nafikova E.P., Rakhmeyev R.G., Galeev R.V., Komolov A.S.

The energies of formation and dissociative decays of temporary negative ions of the organophosphorus insecticide chlorpyrifos are studied using electron transmission, dissociative electron attachment spectroscopies and quantum-chemical calculations.

Faizullin M.G., Galeev R.V., Mamleev A.K.

Vibrational satellites caused by pseudorotation are identified in the microwave spectrum of 2-methyl-1,3-dioxolane. The rotational constants of the satellites are determined up to state v = 6. Splittings between lower pseudorotational energy levels are determined by measuring the relative intensities of rotational transitions. An attempt is made to determine the form of the pseudorotation function of the molecule using the obtained data.

Faizullin M.G., Galeev R.V., Mamleev A.K.

The microwave spectrum of 2-methyltetrahydrofuran in the ground vibrational state is studied. Rotational transitions belonging to one conformer of the molecule are found; no lines belonging to other conformers are detected in the spectrum. Such spectroscopic parameters of a molecule as rotational and quartic centrifugal distortion constants are determined using a set of identified rotational transitions in the quasirigid rotor approximation. Components of the dipole moment of a molecule in the principal axes system are determined from the Stark effect for four rotational transitions. Stable conformations of the molecule are sought by means of B3PW91 and B3LYP with aug-cc-pVXZ (X = D, T, Q) basis sets. A possible stable conformation of the molecule is discussed.

Mamleev A.K., Galeev R.V., Faizullin M.G.

The microwave spectrum of 2,5-dimethyl-1,3-dioxane is studied. The spectrum is identified to have the a and c type rotational transitions of the trans- and cis-isomers of the molecule. The experimental frequencies of the transitions are used to calculate the rotational constants and the quartic centrifugal distortion constants of the isomers. The dipole moments are determined. Quantum chemical calculations are performed by the B3PW91/aug-cc-pVDZ density functional method. The calculated results are compared with the experimental data. The equilibrium geometries of 1,3-dioxane and 2-methyl-, 5-methyl-, and 2,5-dimethyl-1,3-dioxanes are compared. It is found that the alkyl substitution leads to a change in the ring geometry

Mamleev A.K., Galeev R.V., Faizullin M.G.

In the microwave spectrum of 4,4-dimethyl-1,3-dioxane, the rotational transitions of a, b, and c types with J ≤ 54 are identified in the ground vibrational state of the molecule in the frequency range of 12 GHz to 37 GHz. Rotational constants, quartic centrifugal distortion constants, and the dipole moment of the molecule are determined. The revealed transitions are found to belong to the chair conformer. The B3PW91/aug-cc-pVDZ method is used to calculate the geometric parameters of 1,3-dioxane, 4-methyl-1,3-dioxane, and 4,4-dimethyl-1,3-dioxane. Alkyl substitution is shown to cause changes in the geometry of the 1,3-dioxane core.

Mamleev A.K., Gunderova L.N., Galeev R.V., Shapkin A.A., Faizullin M.G., Nikitina A.P., Shornikov D.V.

In the microwave spectrum of a 5-methyl-1,3-dioxane sample, the rotational transitions of a and c types with 4 ≤ J ≤ 11 for five isotopomers of a molecule with 13C and 18O isotopes in different sites are identified in a frequency range of 18 GHz to 42 GHz. The spectroscopic constants of isotopomers are found. The substituted r s and effective r o structural parameters of 5-methyl-1,3-dioxane are determined. By the B3PW91/aug-cc-pVDZ density functional method the equilibrium structure of the molecule is calculated. The results of quantum chemical calculations are compared to the experimental data.

Mamleev A.K., Galeev R.V., Gunderova L.N., Faizullin M.G., Shapkin A.A.

The microwave spectrum of 5-methyl-1,3-dioxane was studied in the frequency range 12–35 GHz. The a and c type rotation transitions with J≤30 were identified. The rotational constants A = 4658.5244(33) MHz, B = 2383.3930(12) MHz, and C = 1724.28907(88) MHz and the quartic constants of the centrifugal distortion of the molecule in the ground vibrational state were determined. The components of the dipole moment were found, μ a = 1.76 ± 0.01 D and μ c = 1.10 ± 0.01 D; the net dipole moment of the molecule is μ = 2.08 ± 0.01 D. 5-Methyl-1,3-dioxane was calculated by the B3PW91/aug-cc-pVDZ density functional theory method. The calculated data are compared with the experimental data. The most stable conformation is the chair conformation with an equatorial orientation of the methyl group.

Mamleev A.K., Gunderova L.N., Galeev R.V., Shapkin A.A., Faizullin M.G., Nikitina A.P., Shornikov D.V., Kantor E.A.

The microwave spectra of five isotopomers with the 13C and 18O natural abundance isotopes of the 2-methyl-1,3-dioxane molecule (22–50 GHz) were studied. Rotational transitions of a and c types with 4 ≤ J ≤ 12 were identified. The rotational constants and the substitution r s and effective r o structural parameters of the molecule were determined. Ab initio calculations on 2-methyl-1,3-dioxane were performed with molecular structure optimization. The results of quantum-chemical calculations at different levels are compared with experimental data.

Mamleev A.K., Galeev R.V., Gunderova L.N., Faizullin M.G., Shapkin A.A.

The microwave spectrum of 4-methyl-1,3-dioxane is studied in a frequency range from 16 GHz to 40 GHz. The rotational transitions of a-, b-, and c-types with J ≤ 57 are identified. The rotational constants (MHz) A = 4802.335(2), B = 2376.163(1), C = 1738.852(1) and the quartic constants of the centrifugal distortion are found for the ground vibrational state of the molecule. The components of the dipole moment (D) μ a = 0.73(1), μb = 1.32(1), μc = 1.36(1) and the total dipole moment μ = 2.03(1) are determined. The experimental data obtained correspond to the chair conformation of the molecule with the equatorial orientation of the methyl group.

Mamleev A.K., Gunderova L.N., Galeev R.V., Shapkin A.A., Faizullin M.G., Gorbunova N.V., Shornikov D.V., Kantor E.A.

Microwave spectra of the 1,3-dioxane molecule (C4H8O2) with the main isotopic composition and four its isotopomers (13C(2)12C3H8 16O2, 13C(4)12C3H8 16O2, 13C(5)12C3H8 16O2, 18O(1)12C4H8 16O) are investigated in a frequency range of 28–44 GHz. Rotational transitions of b-and c-types with 2 ≤ J ≤ 5 are identified. Rotational constants, quartic constants of centrifugal distortion, isotope-substituted r s-and effective r 0-structures of the molecule ring are determined. Experimental data are compared to the results of quantum chemical calculations of different levels.

Dim C.A., Sorrells C., Hernandez-Castillo A.O., Crabtree K.N.

Izadi F., Luxford T.F., Sedmidubská B., Arthur-Baidoo E., Kočišek J., Ončák M., Denifl S.

Abstract2‐Bromo‐1‐(3,3‐dinitroazetidin‐1‐yl)ethan‐1‐one (RRx‐001) is a hypoxic cell chemotherapeutics with already demonstrated synergism in combined chemo‐radiation therapy. The interaction of the compound with secondary low‐energy electrons formed in large amounts during the physico‐chemical phase of the irradiation may lead to these synergistic effects. The present study focuses on the first step of RRx‐001 interaction with low‐energy electrons in which a transient anion is formed and fragmented. Combination of two experiments allows us to disentangle the decay of the RRx‐001 anion on different timescales. Sole presence of the electron initiates rapid dissociation of NO2 and HNO2 neutrals while NO2− and Br− anions are produced both directly and via intermediate complexes. Based on our quantum chemical calculations, we propose that bidirectional state switching between π*(NO2) and σ*(C−Br) states explains the experimental spectra. The fast dynamics monitored will impact the condensed phase chemistry of the anion as well.

Izadi F., Luxford T.F., Sedmidubská B., Arthur-Baidoo E., Kočišek J., Ončák M., Denifl S.

Abstract2‐Bromo‐1‐(3,3‐dinitroazetidin‐1‐yl)ethan‐1‐on (RRx‐001) ist ein Chemotherapeutikum für sauerstoffarme Tumore und zeigte bereits Synergieeffekte in Kombination mit Strahlentherapie. Die Wechselwirkung des Moleküls mit niederenergetischen Sekundärelektronen, die in großer Zahl in der physikalisch‐chemischen Phase der Bestrahlung gebildet werden, könnten für diesen Synergieeffekt verantwortlich sein. Die vorliegende Studie konzentriert sich auf die ersten Schritte in der Wechselwirkung von RRx‐001 mit niederenergetischen Elektronen, in denen das temporäre negative Ion gebildet wird und rasch fragmentiert. Die Kombination von Resultaten zweier Versuchsaufbauten erlaubt es uns, den Zerfall des RRx‐001 Anions auf verschiedenen Zeitskalen zu entflechten. Die alleinige Anwesenheit des eingefangenen Elektrons führt zu einer raschen Abspaltung von NO2 und HNO2, während NO2− und Br− Anionen direkt beziehungsweise über andere Zwischenprodukte gebildet werden. Auf Basis quantenchemischer Rechnungen schlagen wir einen bidirektionalen Wechsel zwischen π*(NO2) und σ*(C−Br) Zuständen vor, welcher die experimentellen Spektren erklärt. Die beobachtete schnelle Dynamik lässt auch Schlussfolgerungen für die Chemie des Anions in der kondensierten Phase zu.

Chen J., Pelc A., Ameixa J., Kossoski F., Denifl S.

Mohaček-Grošev V.

The conformation of tetrahydrofuran (THF) molecules in vapor has been the subject of considerable computational and experimental studies, the most recent by Park and Kwon stated that the difference between the most stable, twisted C2 conformer and the bent Cs conformer is 17 ± 15 cm−1. Because of low symmetry, all modes from both conformers are allowed in the Raman and infrared spectra. In 1982, Aleksanyan and Antipov observed the emergence of two Raman bands at 249 and 303 cm−1 at 20 K, while only one band at 293 cm−1 was present in solid THF at 142. They assigned the 249 cm−1 band to the restricted pseudorotational motion of THF in the solid state, because on heating, the band diminishes and is too weak to be observed near melting point (at 142 K). Cadioli et al. reported a study of the vibrational spectrum of tetrahydrofuran, giving a complete assignment of all bands including those present in the low-temperature Raman spectrum at 85 K and infrared bands observed at 90 K. They assigned the band at 242 cm−1 in the Raman spectrum at 85 K as an overtone of the lowest normal mode (pseudorotational mode), while the 299 cm−1 band in the same spectrum was assigned as a radial mode. In the following, low-temperature Raman spectra of solid THF together with the Raman matrix isolated spectrum of THF in air will be presented and compared to published data. Our results indicate that the band observed at 245 cm−1 at 10 K is too strong to be assigned as an overtone, since its intensity is of the same magnitude as the 299 cm−1 band.

Böhmer T., Pabst F., Gabriel J.P., Blochowicz T.

Silva W., van Wijngaarden J.

AbstractThe influence of the hydroxymethyl (CH2OH) group on the tetrahydrofuran (THF) ring structure was investigated by disentangling the gas phase conformational landscape of the sugar analogue tetrahydrofurfuryl alcohol (THFA). By combining rotational spectroscopy (6–20 GHz) and quantum chemical calculations, transitions corresponding to two stable conformers of THFA and their 13C isotopologues were observed and assigned in the rotational spectrum. The positions of the C atoms were precisely determined to unambiguously distinguish between nearly isoenergetic pairs of conformers that differ in their ring configurations: envelope (E) versus twist (T). The rotational spectrum confirms that the E ring geometry is favoured when the CH2OH fragment lies gauche (−) to the THF backbone (OCCO ~−60°) whereas the T form is more stable for the gauche (+) alignment of the substituent (OCCO ~+60°). The observed spectral intensities suggest that conformational relaxation of the THF geometry (E↔T) to the more stable form readily occurs within the pairs of g− and g+ conformers which is consistent with the low barriers (1.5–1.7 kJ mol−1) for conversion determined via transition state calculations. Insights into the intramolecular hydrogen bonding and other weak interactions stabilizing the lowest energy structures of THFA were derived and rationalized using non‐covalent interaction analyses.

Park S.M., Kwon C.H.

Tetrahydrofuran (THF) has garnered significant attention due to its pivotal role in biological and chemical processes. The diverse array of conformations exhibited by THF profoundly impacts its reactivity and interactions with other molecules. Understanding these conformational preferences is crucial for comprehending its molecular behavior. In this study, we utilize infrared (IR) resonant vacuum ultraviolet photoionization/mass-analyzed threshold ionization (VUV-PI/MATI) mass spectroscopies to capture distinctive vibrational spectra of individual conformers, namely, “twisted” and “bent,” within THF. Our conformer-specific vibrational spectra provide valuable insights into the relative populations of these two conformers. The analysis reveals that the twisted (C2) conformer is more stable than the bent (CS) conformer by 17 ± 15 cm−1. By precisely tuning the VUV photon energy to coincide with vibrational excitation via IR absorption, we selectively ionize specific conformers, yielding two-photon IR + VUV-PI/MATI spectra corresponding to the twisted and bent conformers. This investigation conclusively affirms that both the twisted and bent conformers coexist in the neutral state, while only the twisted conformer exists in the cationic state. These findings not only bridge gaps in existing knowledge but also provide profound insights into the behavior of this pivotal molecule in the realms of biology and medicine.

Aitken R.A.

This review covers work published in the calendar year 2022. The synthesis and reaction chemistry of five-membered heterocycles containing two oxygen atoms, two sulfur atoms, or an oxygen and a sulfur are reviewed.

Hänni N., Altwegg K., Baklouti D., Combi M., Fuselier S.A., De Keyser J., Müller D.R., Rubin M., Wampfler S.F.

The puzzling complexity of terrestrial biomolecules is driving the search for complex organic molecules in the interstellar medium (ISM) and serves as a motivation for many in situ studies of reservoirs of extraterrestrial organics, from meteorites and interplanetary dust particles to comets and asteroids. Comet 67P/Churyumov-Gerasimenko (67P), the best-studied comet to date, has been visited and accompanied for 2 yr by the European Space Agency’s Rosetta spacecraft. Around 67P’s perihelion and under dusty conditions, the high-resolution mass spectrometer on board Rosetta has provided a spectacular glimpse into this comet’s chemical complexity. For this work, we analyzed the O-bearing organic volatiles in unprecedented detail. Through a comparison of 67P’s inventory with molecules detected in the ISM, in other comets, and in soluble organic matter extracted from the Murchison meteorite, we also highlight the (pre)biotic relevance of different chemical groups of species. We report first evidence for abundant extraterrestrial O-bearing heterocycles (with abundances relative to methanol often on the order of 10% and a relative error margin of 30–50%) and various representatives of other molecule classes, such as carboxylic acids and esters, aldehydes, ketones, and alcohols. As with the pure hydrocarbons, some hydrogenated forms seem to be dominant over their dehydrogenated counterparts. An interesting example is tetrahydrofuran, as it might be a more promising candidate for searches in the ISM than the long-sought furan. Our findings not only support and guide future efforts to investigate the origins of chemical complexity in space, but they also strongly encourage the study, in the laboratory as well as by modeling, of such topics as the ratios of unbranched versus branched species and hydrogenated versus dehydrogenated species in astrophysical ice analogs.

Milesevic D., Stimson J., Popat D., Robertson P.A., Vallance C.

Tetrahydrofuran (THF) can be considered the simplest analog of the deoxyribose backbone component of deoxyribonucleic acid. As such, it provides a useful model for probing the photochemistry of such biomolecular...

Asfandiarov N.L., Muftakhov M.V., Pshenichnyuk S.A.

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 (Mˉ). The autodetachment lifetime of Mˉ was measured to be about 170 μs for both compounds. The widths of the Mˉ 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.

Asfandiarov N.L., Muftakhov M.V., Pshenichnyuk S.A.

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).

Faizullin M.G., Galeev R.V.

Microwave spectroscopy is used to study the microwave rotational spectrum of a 2-methyltetrahydrofuran molecule in three excited states of hindered pseudorotation. The rotational constants and components of the molecule’s dipole moment in these states are determined. An attempt is made to determine the shape of the potential curve of the molecule’s hindered pseudorotation, based on these data and the results from quantum-chemical calculations.

Kurilova E.I., Kantor E.A.

Asfandiarov N.L., Muftakhov M.V., Rakhmeev R.G., Safronov A.M., Markova A.V., Pshenichnyuk S.A.

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 μs were observed in all molecules under investigation. In all cases molecular anion fragmentation is poor: only the Brˉ, [M-Br]ˉ and (with very small intensity) [M-H]ˉ 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 (τ a =26 μs and τ a =25 μs, respectively) does not contradict the fact that their dissociation rates measured by the pulse radiolysis method are fairly large (1.0 ×10 10 s −1 and 1.8 ×10 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 ~1.93 Å. 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.

Asfandiarov N.L., Muftakhov M.V., Pshenichnyuk S.A., Rakhmeev R.G., Safronov A.M., Markova A.V., Vorob’ev A.S., Luxford T.F., Kočišek J., Fedor J.

The present work combines experiment and theory to reveal the behavior of bromo-substituted-biphenyls after an electron attachment. We experimentally determine anion lifetimes using an electron attachment–magnetic sector mass spectrometer instrument. Branching ratios of dissociative electron attachment fragments on longer timescales are determined using the electron attachment–quadrupole mass spectrometer instrument. In all cases, fragmentation is low: Only the Br− and [M–Br]− ions are detected, and [M–H]− is observed only in the case of 4-Br-biphenyl and parent anion lifetimes as long as 165 µs are observed. Such lifetimes are contradictory to the dissociation rates of 2- and 4-bromobiphenyl, as measured by the pulse radiolysis method to be 3.2 × 1010 and >5 × 1010 s−1, respectively. The discrepancy is plausibly explained by our calculation of the potential energy surface of the dissociating anion. Isolated in vacuum, the bromide anion can orbit the polarized aromatic radical at a long distance. A series of local minima on the potential energy surface allows for a roaming mechanism prolonging the detection time of such weakly bound complex anions. The present results illuminate the behavior recently observed in a series of bromo-substituted compounds of biological as well as technological relevance.

Pshenichnyuk S.A., Asfandiarov N.L., Vorob’ev A.S., Matejčík Š.

Abstract The latest achievements are presented in experimental and theoretical studies of resonance scattering of low-energy (0–15-eV) electrons from molecular targets in a gas phase resulting in the formation and decay of negative ions. The focus is on dissociative electron attachment spectroscopy for studying the microsecond dynamics of molecules containing an excess electron. Some studies of fundamental processes in isolated negative ions containing up to several electronvolts of excess energy are briefly described, and the possibility of using the results in interdisciplinary fields is discussed. A goal of the paper is to attract attention to the above-mentioned studies, which are rapidly developing abroad but only scarcely presented in the domestic literature.

Cipriani M., Bjornsson R., Barclay M., Terfort A., Fairbrother D.H., Ingólfsson O.

A combined theoretical and experimental study on the fragmentation of the mono-halogenated biphenyls; 2-chlorobiphenyl, 2-bromobiphenyl and 2-iodobiphenyl upon electron impact is presented. The appearance energies of the fragments observed and the energy dependence of their relative cross sections are reported. This is a follow up on our previous report (Barclay et al., 2019) [ 24 ] on the influence of the dihedral angle on the ionization energy of these compounds, but here we report the appearance energies and the energy dependence of the relative cross-section for all the major fragments. The appearance energies are compared to quantum mechanical threshold calculations at the coupled cluster level of theory and possible molecular structures and reaction pathways are discussed for the observed m/z ratios. For the loss of the halogen along with 1–2 H the agreement between the experiment and theory is good as reported earlier. However, the discrepancy is considerably larger for the ring rupture channels.

Suits A.G.

Roaming reactions were first clearly identified in photodissociation of formaldehyde 15 years ago, and roaming dynamics are now recognized as a universal aspect of chemical reactivity. These reactions typically involve frustrated near-dissociation of a quasibound system to radical fragments, followed by reorientation at long range and intramolecular abstraction. The consequences can be unexpected formation of molecular products, depletion of the radical pool in chemical systems, and formation of products with unusual internal state distributions. In this review, I examine some current aspects of roaming reactions with an emphasis on experimental results, focusing on possible quantum effects in roaming and roaming dynamics in bimolecular systems. These considerations lead to a more inclusive definition of roaming reactions as those for which key dynamics take place at long range.

Asfandiarov N.L., Pshenichnyuk S.A., Rakhmeyev R.G., Tuktarov R.F., Zaitsev N.L., Vorob’ev A.S., Kočišek J., Fedor J., Modelli A.

Electron attachment to the 4-bromobiphenyl molecule and the decay channels of its molecular anion were investigated by means of Dissociative Electron Attachment (DEA) spectroscopy with two different spectrometers. The first apparatus is equipped with a static magnet mass analyzer (Ufa group) and the second one with a quadrupole mass filter (Prague group). The dominant DEA channel at low electron energy leads to formation of Br− negative fragments. Long-lived (τa = 40 µs at the temperature of 80 °C) molecular negative ions were detected only in the Ufa experiment. We explored the involved potential energy surfaces and found that the molecular anion has two distinct structures with the C–Br distances of 1.92 Å and 2.8 Å. The statistical model based on the Arrhenius approximation fully explains the experimental observations and sheds light on the earlier anion dissociation kinetic studies in solution.

Faizullin M.G., Galeev R.V., Mamleev A.K.

Vibrational satellites caused by pseudorotation are identified in the microwave spectrum of 2-methyl-1,3-dioxolane. The rotational constants of the satellites are determined up to state v = 6. Splittings between lower pseudorotational energy levels are determined by measuring the relative intensities of rotational transitions. An attempt is made to determine the form of the pseudorotation function of the molecule using the obtained data.

Chen E.S., Chen E.C.

Pshenichnyuk S.A., Modelli A., Komolov A.S.

Small molecular species present in mitochondria as, e.g. quinones and oxygen, can capture cellular electrons thus behaving as electron carriers or reactive species, supporting the fundamental proce...

Asfandiarov N.L., Muftakhov M.V., Pshenichnyuk S.A., Papp P., Danko M., Lacko M., Blaško J., Matejčik Š., Modelli A.

2,4,6-trichloroanisole and 2,4,6-tribromoanisole were investigated by means of electron transmission spectroscopy and two different types of dissociative electron attachment spectrometers. The results obtained were interpreted with the support of density functional theory calculations. The dominant dissociative decay channels of the temporary molecular negative ions lead to the formation of Cl− and Br− in the low electron energy region. Formation of long-lived parent anions is observed at thermal electron energies. Their relative intensity depends on the experimental time window, ∼36 μs in the case of the static magnet mass analyzer and ∼200 μs for the quadrupole mass analyzer employed. The results obtained may be useful for rapid detection of these compounds in wine and pharmaceutical industries, as well as other branches connected to the food industry, e.g., packaging.

Koch S., Kaiser C.D., Penner P., Barclay M., Frommeyer L., Emmrich D., Stohmann P., Abu-Husein T., Terfort A., Fairbrother D.H., Ingólfsson O., Gölzhäuser A.

The determination of the negative ion yield of 2′-chloro-1,1′-biphenyl (2-Cl-BP), 2′-bromo-1,1′-biphenyl (2-Br-BP) and 2′-iodo-1,1′-biphenyl (2-I-BP) upon dissociative electron attachment (DEA) at an electron energy of 0 eV revealed cross section values that were more than ten times higher for iodide loss from 2-I-BP than for the other halogenides from the respective biphenyls (BPs). Comparison with dissociative ionization mass spectra shows that the ratio of the efficiency of electron impact ionization induced fragmentation of 2-I-BP, 2-Br-BP, and 2-Cl-BP amounts to approximately 1:0.7:0.6. Inspired by these results, self-assembled monolayers (SAMs) of the respective biphenyl-4-thiols, 2-Cl-BPT, 2-Br-BPT, 2-I-BPT as well as BPT, were grown on a Au(111) substrate and exposed to 50 eV electrons. The effect of electron irradiation was investigated by X-ray photoelectron spectroscopy (XPS), to determine whether the high relative DEA cross section for iodide loss from 2-I-BPT as compared to 2-Br-BP and 2-Cl-BP is reflected in the cross-linking efficiency of SAMs made from these materials. Such sensitization could reduce the electron dose needed for the cross-linking process and may thus lead to a significantly faster conversion of the respective SAMs into carbon nanomembranes (CNMs) without the need for an increased current density. XPS data support the notation that DEA sensitization may be used to achieve more efficient electron-induced cross-linking of SAMs, revealing more than ten times faster cross-linking of 2-I-BPT SAMs compared to those made from the other halogenated biphenyls or from native BPT at the same current density. Furthermore, the transfer of a freestanding membrane onto a TEM grid and the subsequent investigation by helium ion microscopy (HIM) verified the existence of a mechanically stable CNM created from 2-I-BPT after exposure to an electron dose as low as 1.8 mC/cm2. In contrast, SAMs made from BPT, 2-Cl-BPT and 2-Br-BPT did not form stable CNMs after a significantly higher electron dose of 9 mC/cm2.

Faizullin M.G., Galeev R.V., Mamleev A.K.

The microwave spectrum of 2-methyltetrahydrofuran in the ground vibrational state is studied. Rotational transitions belonging to one conformer of the molecule are found; no lines belonging to other conformers are detected in the spectrum. Such spectroscopic parameters of a molecule as rotational and quartic centrifugal distortion constants are determined using a set of identified rotational transitions in the quasirigid rotor approximation. Components of the dipole moment of a molecule in the principal axes system are determined from the Stark effect for four rotational transitions. Stable conformations of the molecule are sought by means of B3PW91 and B3LYP with aug-cc-pVXZ (X = D, T, Q) basis sets. A possible stable conformation of the molecule is discussed.

Rathod A.L., Garg R.K.

• This review introduces the severity of death occurred due to chlorpyrifos poisoning in India.

Pshenichnyuk S.A., Komolov A.S.

The polychlorinated compounds captafol (CPL) and 2,6-dichloroisonicotinic acid (INA) are able to protect plants acting as a fungicide or an inductor of plant resistance, respectively. At the same time, CPL and INA are dangerous for the respiratory organisms, i.e. mammalians, bacteria, and fungi. The high electron-withdrawing ability of these compounds enables them to serve as unnatural electron acceptors in the cellular ambient near to electron transport pathways located in the thylakoid membrane of chloroplasts or in the mitochondrial respiratory chain. Low-energy electron attachment to CPL and INA in vacuo leads to formation of many fragment species mainly at thermal electron energy as it is shown using dissociative electron attachment spectroscopy. On the basis of the experimental findings, assigned with the support of density functional theory calculations it is suggested that the different bioactivity of CPL and INA in respiratory and photosynthetic organisms is due to the interplay between the dissociative electron attachment process and the energies of electrons leaked from the electron transport pathways.

Van V., Stahl W., Nguyen H.V.

The rotational spectra of 2-methyltetrahydrofuran have been observed using a pulsed molecular beam Fourier transform microwave spectrometer operating in the frequency range 2–26.5 GHz. Conformational analysis using quantum chemical calculations yields two stable conformers; both of them possess an envelope structure. The conformational transformation can occur via two different transition states. The Cremer-Pople notation for five-membered rings is chosen for describing the conformations. Only one conformer with equatorial position of the methyl group is assigned in the experimental spectrum. The fits of its parent species, 13 C- and 18 O-isotopologues result in highly accurate molecular parameters, and enable the determination of a heavy atom r s structure using Kraitchman’s equations. This experimentally determined structure is in excellent agreement with the structure calculated by anharmonic frequency calculations.