Infrared spectroscopy of the α-hydroxyethyl radical isolated in cryogenic solid media.

The α-hydroxyethyl radical (CH3·CHOH, 2A) is a key intermediate in ethanol biochemistry, combustion, atmospheric chemistry, radiation chemistry, and astrochemistry. Experimental data on the vibrational spectrum of this radical are crucially important for reliable detection and understanding of the chemical dynamics of this species. This study represents the first detailed experimental report on the infrared absorption bands of the α-hydroxyethyl radical complemented by ab initio computations. The radical was generated in solid para-H2 and Xe matrices via the reactions of hydrogen atoms with matrix-isolated ethanol molecules and radiolysis of isolated ethanol molecules with x rays. The absorption bands with maxima at 3654.6, 3052.1, 1425.7, 1247.9, 1195.6 (1177.4), and 1048.4 cm-1, observed in para-H2 matrices appearing upon the H· atom reaction, were attributed to the OHstr, α-CHstr, CCstr, COstr + CCObend, COstr, and CCstr + CCObend vibrational modes of the CH3·CHOH radical, respectively. The absorption bands with the positions slightly red-shifted from those observed in para-H2 were detected in both the irradiated and post-irradiation annealed Xe matrices containing C2H5OH. The results of the experiments with the isotopically substituted ethanol molecules (CH3CD2OH and CD3CD2OH) and the quantum-chemical computations at the UCCSD(T)/L2a_3 level support the assignment. The photolysis with ultraviolet light (240-300 nm) results in the decay of the α-hydroxyethyl radical, yielding acetaldehyde and its isomer, vinyl alcohol. A comparison of the experimental and theoretical results suggests that the radical adopts the thermodynamically more stable anti-conformation in both matrices.

Astrochemically Relevant Radicals and Radical-Molecule Complexes: A New Insight from Matrix Isolation.

The reactive open-shell species play a very important role in the radiation-induced molecular evolution occurring in the cold areas of space and presumably leading to the formation of biologically relevant molecules. This review presents an insight into the mechanism of such processes coming from matrix isolation studies with a main focus on the experimental and theoretical studies performed in the author's laboratory during the past decade. The radicals and radical cations produced from astrochemically relevant molecules were characterized by Fourier transform infrared (FTIR) and electron paramagnetic resonance (EPR) spectroscopy. Small organic radicals containing C, O, and N atoms are considered in view of their possible role in the formation of complex organic molecules (COMs) in space, and a comparison with earlier results is given. In addition, the radical-molecule complexes generated from isolated intermolecular complexes in matrices are discussed in connection with their model significance as the building blocks for COMs formed under the conditions of extremely restricted molecular mobility at cryogenic temperatures.

Radiation-induced transformations of matrix-isolated ethanol molecules at cryogenic temperatures: an FTIR study.

Ethanol (C2H5OH) is one of the most common alcohol molecules observed in various space media (molecular clouds, star formation regions, and, highly likely, interstellar ices), where it is exposed to light and ionizing radiation, leading to more complex organic molecules and eventually to the biologically important species. To better understand the radiation-induced evolution of ethanol molecules in icy media, we have examined the transformations of isolated C2H5OH and C2D5OH under the action of X-rays and vacuum ultraviolet (VUV) radiation in solid inert matrices (Ne, Ar, Kr, and Xe) at 4.4 K using Fourier transform infrared (FTIR) spectroscopy. The results obtained with X-ray irradiation demonstrate the formation of a variety of radiolysis products corresponding to dehydrogenation (CH3CHOH˙, CH3CHO, CH2CHOH, CH3CO˙, H2CCO-H2, H2CCO, HCCO˙, CCO) and C-C bond rupture (H2CO, HCO˙, CO, CH4, and CH3˙). The absorptions of the CH3CHOH˙ radical related to the CCO stretching (the bands at 1249.1, 1247.0, 1246.2, and 1245.1 cm-1, in Ne, Ar, Kr, and Xe, respectively) were first tentatively characterized on the basis of comparison with available computational data. In addition, the C2H2⋯H2O complex, which corresponds to dehydrogenation, was found followed by C-O bond cleavage. The results were confirmed by experiments with isotopic substitution. It was found that dehydrogenation strongly predominated in a xenon matrix, while skeleton bond rupture is more feasible in neon and argon. The matrix effect was attributed to a significant role of "hot" reaction channels in neon and argon, which are efficiently quenched due to relaxation in more polarizable xenon. The VUV photolysis (185 nm) in Ar and Xe matrices yields a similar set of products, except for CH3CHOH˙ and CH2CHOH, which were not found (the nonobservation of the former species may be explained by its efficient secondary photolysis). The plausible mechanisms of product formation and astrochemical implications of the results are discussed.

Reactions of oxygen atoms with fluoroform and its radiolysis products: matrix isolation and ab initio study.

The investigation of the reactions of oxygen atoms with fluoroform (CHF3) molecules and products of their degradation present significant interest for better understanding of the impact of chemically inert fluorinated compounds on atmospheric chemistry and may provide a deeper insight into mechanisms of chemical processes occurring under the action of hard UV and ionizing radiation. In the present study we applied a matrix isolation technique with FTIR spectroscopic detection combined with ab initio calculations to address this issue. It was found that the reactions of "hot" (translationally excited) O(1D) atoms produced by X-ray or UV radiation from appropriate precursors (N2O or H2O) resulted in the formation of carbonyl fluoride (COF2) and its complex with HF. The complex was detected and characterized for the first time. Singlet oxygen atoms also probably react with the products of radiation-induced degradation of fluoroform (CF3 and CF2). Additionally, the reaction of "hot" O(3P) atoms with fluoroform may occur to a certain extent yielding the CF3 radical. No evidence for the reactions of thermal O(3P) atoms with CHF3 or products of its degradation was found under the experimental conditions used. The implications of the results of this model study for understanding the evolution of fluoroform in the upper layers of the stratosphere and ionosphere are discussed.

An EPR study on the radiolysis of isolated ethanol molecules in solid argon and xenon: matrix control of radiation-induced generation of radicals in cryogenic media.

This paper addresses the basic question of the impact of a chemically inert environment on the radiation-induced transformations of isolated organic molecules in icy media at cryogenic temperatures with possible implications for astrochemical issues. The radicals produced by X-ray irradiation of isolated ethanol molecules (C2H5OH and CH3CD2OH) in solid argon and xenon matrices at 7 K were characterized by electron paramagnetic resonance (EPR) spectroscopy. It was shown that methyl (CH3˙) and formyl (HCO˙) radicals resulting from the C-C bond cleavage were mainly produced in the case of solid argon, which was attributed to the significant role of "hot" ionic fragmentation and inefficient energy dissipation to medium. In contrast, irradiation in xenon results in the predominant formation of α-hydroxyethyl radicals (CH3˙CHOH or CH3˙CDOH(D) in the cases of C2H5OH and CH3CD2OH, respectively). Remarkably, the experiments with selectively deuterated ethanol provide strong indirect evidence for the primary formation of ethoxy (CH3CD2O˙) radicals due to O-H bond cleavage, which convert to the α-hydroxyethyl radicals due to isomerization occurring at 7 K. The α-hydroxyethyl radicals adopt a specific rigid conformation with a non-rotating methyl group at low temperatures, which is an unusual effect for neutral CH3˙CHX species, and exhibit free rotation in solid xenon only at ca. 65 K.

Radiation-induced transformation of the C2H2⋯NH3 complex in cryogenic media: Identification of C2H2⋯NH2 ∙ complex and evidence of cold synthetic routes.

Acetylene and ammonia are important constituents of the interstellar medium, and their coupled chemistry induced by high-energy radiation may be responsible for the formation of a variety of prebiotically important organic-nitrogen compounds. In this work, we first comprehensively characterized the vibrational spectrum of the 1:1 C2H2⋯NH3 complex obtained by deposition of the C2H2/NH3/Ng (Ng = Ar, Kr, or Xe) gaseous mixtures at 5 K using Fourier transform infrared spectroscopy and ab initio calculations at the CCSD(T)/L2a_3 level of theory and examined its radiation-induced transformations. The parent complex adopts a C3v symmetric top molecular structure with C2H2 acting as a proton donor. The x-ray-induced transformations of this complex result in the formation of the C2H2⋯NH2 ∙ complex and various CN-containing species (CH2CNH, CH3NC, CH2NCH, CH2NC∙, CCN∙, and CNC∙). The radical-molecule complex was identified based on comparison of experimental data with the results of the UCCSD(T)/L2a_3 computations. It is characterized by distinct features in the region of acetylene CHasym str mode, red-shifted from the corresponding absorptions of non-complexed acetylene by -72.9, -70.4, and -60.6 cm-1 for Ar, Kr, and Xe, respectively. Additionally, in krypton and xenon matrices, the blue-shifted features in the CHasym bend region of acetylene were observed, which can be also tentatively attributed to the C2H2⋯NH2 ∙ complex. The extrapolated to the complete basis set limit unrestricted coupled cluster method with single and double, and perturbative triple excitations binding energy of the C2H2⋯NH2 ∙ complex (including zero-point vibration energy correction) is lower than that of the C2H2⋯NH3 complex (1.90 and 2.51 kcal mol-1, respectively). We believe that the C2H2⋯NH2 ∙ complex may be an important intermediate in cold synthetic astrochemistry.

Assembling of Metal-Polymer Nanocomposites in Irradiated Solutions of 1-Vinyl-1,2,4-triazole and Au(III) Ions: Features of Polymerization and Nanoparticles Formation.

Gold nanoparticles (AuNPs) stabilized with poly(1-vinyl-1,2,4-triazole) (PVT) have been synthesized via a one-pot manner in irradiated solutions of 1-vinyl-1,2,4-triazole (VT) and Au(III) ions. The transmission electron microscopy examinations have shown that the sizes of nanoparticles formed range from 1 to 11 nm and are affected by the ratio of VT to gold ions. To study the kinetics peculiarities of the VT polymerization and assembling of AuNPs, UV-Vis spectroscopy was used. The analysis of the data obtained reveals that an inhibition period, influenced by Au(III) concentration, is followed by the polymerization of a monomer. Importantly, the absorbed doses, corresponding to the onset of rapid polymerization, correlate with the doses at which the accelerated formation of AuNPs begins. The kinetics aspects, which could lead to such an effect, are discussed.

The Radiation Chemistry of NH3···CO Complex in Cryogenic Media as Studied by Matrix Isolation.

The NH3···CO complex can be considered an important building block for cold synthetic astrochemistry leading to the formation of complex organic molecules, including key prebiotic species. In this work, we have studied the radiation-induced transformations of this complex in Ar, Kr, and Xe matrices using FTIR spectroscopy. On the basis of comparison with the quantum chemical calculations at the CCSD(T)/L2a_3 level of theory, it was found that the initial complex had the configuration with hydrogen bonding through the carbon atom of CO. Irradiation of the matrix isolated complex with X-rays at 6 K leads to the formation of a number of synthetic products, namely, HNCO (in all matrices), formamide NH2CHO, NH2CO, and HNCO-H2 (in argon and krypton). The matrix effect on the product distribution was explained by the involvement of different excited states of the complex in their formation. It was suggested that formamide results from the singlet excited states while other species mainly originate from triplet excited states. The latter states are efficiently populated through ion-electron recombination (in all matrices) and through intersystem crossing (particularly, in xenon). High yield of the recombination triplet states is a feature of the processes induced by high-energy radiation (in contrast to direct photolysis). NCO, CN, and NO were found as minor secondary products at high adsorbed doses. The astrochemical implications of the obtained results are discussed.

Formation and Evolution of H2C3O+• Radical Cations: A Computational and Matrix Isolation Study.

The family of isomeric H2C3O+• radical cations is of great interest for physical organic chemistry and chemistry occurring in extraterrestrial media. In this work, we have experimentally examined a unique synthetic route to the generation of H2C3O+• from the C2H2···CO intermolecular complex and also considered the relative stability and monomolecular transformations of the H2C3O+• isomers through high-level ab initio calculations. The structures, energetics, harmonic frequencies, hyperfine coupling constants, and isomerization pathways for several of the most important H2C3O+• isomers were calculated at the UCCSD(T) level of theory. The complementary FTIR and EPR studies in argon matrices at 5 K have demonstrated that the ionized C2H2···CO complex transforms into the E-HCCHCO+• isomer, and this latter species is supposed to be the key intermediate in further chemical transformations, providing a remarkable piece of evidence for kinetic control in low-temperature chemistry. Photolysis of this species at λ = 410-465 nm results in its transformation to the thermodynamically most stable H2CCCO+• isomer. Possible implications of the results and potentiality of the proposed synthetic strategy to the preparation of highly reactive organic radical cations are discussed.

Spectroscopy and radiation-induced chemistry of an atmospherically relevant CH2F2 H2O complex: Evidence for the formation of CF2 H2O complex as revealed by FTIR matrix isolation and ab initio study.

Difluoromethane is considered among the environment friendly alternatives to the ozone depleting chlorofluorocarbons. Due to its chemical inertness and lack of UV absorption above 200 nm, this compound can easily come to the upper layers forming complexes with widely abundant atmospheric components, such as water. The radiation-induced degradation of this compound and its complexes may be significant for reliable prediction of its long-term evolution in the environment as well as for development of new ways for its removal. In this work we have studied the vibrational spectroscopic properties and mechanisms of the radiation-induced decay of the CH2F2⋯H2O under the action of X-rays using matrix isolation FTIR spectroscopy and ab initio calculations. The IR spectrum of the complex in an argon matrix was characterized for the first time and assigned to a hydrogen-bonded structure with a binding energy of 11.1 kJ/mol (2.65 kcal/mol) (CCSD(T)/CBS level of theory). Complexation with water leads to a certain suppression of the efficiency of the radiation-induced decomposition of difluoromethane. The obtained results provide evidence for the radiation-induced formation of previously unreported CF2⋯H2O complex (in addition to other oxygen containing molecules, such as COF2 and CO). As demonstrated by calculations, the new difluorocarbene complex reveals a hydrogen bond and it is characterized by a binding energy of 5.73 kJ/mol (1.37 kcal/mol) (CCSD(T)/CBS level of theory).

Radiation-induced transformations of acetaldehyde molecules at cryogenic temperatures: a matrix isolation study.

Acetaldehyde is one of the key small organic molecules involved in astrochemical and atmospheric processes occurring under the action of ionizing and UV radiation. While the UV photochemistry of acetaldehyde is well studied, little is known about the mechanism of processes induced by high-energy radiation. This paper reports the first systematic study on the chemical transformations of CH3CHO molecules resulting from X-ray irradiation under the conditions of matrix isolation in different solid noble gases (Ne, Ar, Kr, and Xe) at 5 K. CO, CH4, H2CCO, H2CCO-H2, C2H2⋯H2O, CH2CHOH, CH3CO˙, CH3˙, HCCO˙, and CCO were identified as the main radiolysis products. The dominant pathway of acetaldehyde degradation involves C-C bond cleavage leading to the formation of carbon monoxide and methane. The second important channel is dehydrogenation resulting in the formation of ketene, a potentially highly reactive species. It was found that the matrix significantly affected both the decomposition efficiency and distribution of the reaction channels. Based on these observations, it was suggested that the formation of the methyl radical as well as vinyl alcohol and the C2H2⋯H2O complex presumably included a significant contribution of ionic pathways. The decomposition of acetyl radicals under photolysis with visible light leading to the CH3˙-CO radical-molecule pair was observed in all matrices, while the recovery of CH3CO˙ in the dark at 5 K was found only in Xe. This finding represents a prominent example of matrix-dependent chemical dynamics (probably, involving tunnelling), which deserves further theoretical studies. Probable mechanisms of acetaldehyde radiolysis and their implications for astrochemistry, atmospheric chemistry and low-temperature chemistry are discussed.

Direct evidence for a radiation-induced synthesis of acetonitrile and isoacetonitrile from a 1 : 1 CH4HCN complex at cryogenic temperatures: is it a missing link between inorganic and prebiotic astrochemistry?

Nitriles are important constituents of extraterrestrial media. Nitriles are supposed to play a crucial role in prebiotic chemistry occurring in the interstellar medium. In this work, we have investigated the low-temperature radiation-induced transformations of a 1 : 1 CH4HCN complex as a plausible precursor of the simplest nitriles using the matrix isolation approach with FTIR spectroscopic detection. The parent complexes isolated in a noble gas (Ng) matrix were obtained by deposition of the CH4/HCN/Ng gaseous mixture and characterized by comparison of experimental complexation-induced shifts of the HCN fundamentals with the results of the ab initio calculations. It was found that the X-ray irradiation of low-temperature matrices containing the isolated 1 : 1 CH4HCN complex resulted in the formation of acetonitrile (CH3CN) and isoacetonitrile (CH3NC) and it appears to be the first experimental evidence for the formation of C2 nitriles (acetonitrile and isoacetonitrile) from such a "building block". Additionally, a 1 : 1 CH4HNC complex was tentatively assigned to the irradiated Ar and Kr matrices. It is demonstrated that the matrix has a strong effect on the CH3CN/CH3NC yield ratio, which dramatically increases in the row Ar < Kr < Xe. Also, the efficiency of the radiation-induced formation of the CH4HNC complex was shown to decrease from Ar to Kr. It is believed that the proposed pathway for acetonitrile formation may be a significant step in the radiation-induced evolution leading to complex organic molecules and biomolecules under astrochemical conditions. Furthermore, the obtained results provide a prominent example of the impact of very weak intermolecular interactions on the radiation-induced transformations in cold media.

A hydrogen-bonded CHF⋯HF complex: IR spectra and unusual photochemistry.

A hydrogen-bonded CHF⋯HF complex was characterized by FTIR matrix isolation spectroscopy and ab initio calculations. Three possible structures of this complex were found at the coupled-cluster with single, double, and perturbative triple excitations [CCSD(T)/L3a_3] level of theory. The comparison between the experiment and theory reveals that the most stable structure with the binding energy of 6.48 kcal/mol is formed upon x-ray irradiation of isolated CH2F2 molecules in noble gas matrices (Ne, Ar, Xe). This species appears to be the first known intermolecular complex of monofluorocarbene, and its identification was unambiguously proved by IR absorptions corresponding to HF deformation (libration), CF stretching, H-C-F bending, and CH and HF stretching modes. It is worth noting that the corresponding spectral features in an argon matrix were previously tentatively ascribed to CH2F2 +· and HF⋯CHF-· [L. Andrews and F. T. Prochaska, J. Chem. Phys. 70, 4714 (1979)], but the calculations performed in the present study definitely support the re-assignment. The observed CHF⋯HF complex can be converted to the parent CH2F2 under the action of light with λ < 525 nm. The plausible mechanism of this conversion using the conical intersection concept is discussed.

Reactions of radiation-induced electrons with carbon dioxide in inert cryogenic films: matrix tuning of the excess electron interactions in solids.

A single-electron reduction of carbon dioxide is supposed to be an important basic step in various processes, ranging from interstellar chemistry to photocatalytic transformations. In this work, we report an FTIR spectroscopic study on the reactions of carbon dioxide (12CO2 and 13CO2) with the radiation-induced excess electrons in deposited cryogenic matrices with different physical characteristics (Ne, N2, Ar, Xe) occurring at 6 K. The reaction was monitored by the observation of carbon dioxide radical anions. It was found that attachment of excess electrons to CO2 occurred in neon and nitrogen matrices, but not in argon and xenon. In the case of nitrogen, the formation of matrix-related cationic species (N4+˙ and NNCO+˙) was also observed. Since the CO2 molecules have a negative intrinsic electron affinity, it was suggested that the electron attachment to CO2 is controlled by the energy of excess electrons in the solid matrix, which is determined by the value of the corresponding conduction band bottom energy (V0). The implications of the obtained results are discussed.

Radiation-Induced Transformation of CHF3···CO to the CF3···CO Complex: Matrix Isolation and Ab Initio Study.

The X-ray-induced transformations of CHF3/CO/Ar and CHF3/CO/Kr systems were investigated by Fourier transform infrared (FTIR) matrix isolation spectroscopy at 6 K. It was found that addition of CO suppressed decomposition of fluoroform in an Ar matrix, probably because of trapping of matrix holes by CO and CHF3···CO complexes. Considerable increase of the CF3/CF2 ratio with increasing CO content in the matrix was attributed to stabilization of the CF3 radical with respect to further radiation-induced fragmentation because of its complexation with the CO molecule. The CF3···CO complex generated from the CHF3···CO precursor complex was characterized by FTIR spectroscopy and ab initio calculations at the CCSD(T) and MP2 levels of theory. To the best of our knowledge, it is the first experimentally observed complex of the CF3 radical. The computed interaction energy was found to be 0.35 kcal/mol at the CCSD(T)/L2a_3 level (0.36 kcal/mol at the MP2/L2a_3 level), taking into account zero-point energy and basis set superposition error corrections. Despite the very weak intermolecular bonding, the complex is characterized by distinct features in the regions of C-F symmetric and antisymmetric stretching (CF3) and CO stretching (the latter one was observed only in a krypton matrix). The geometrical structure of the radical-molecule complex is close to that of its molecular precursor.

Formation and interconversion of CCN and CNC radicals resulting from the radiation-induced decomposition of acetonitrile in solid noble gas matrices.

Acetonitrile and the species resulting from its dehydrogenation play an important role in the radiation-induced evolution of organic matter in the space environment. In this work, we report on FTIR spectroscopic studies of the degradation of isolated CH3CN and CD3CN molecules induced by prolonged X-ray irradiation in solid noble gas matrices at 5 K. The principal products observed at high conversion degree of the parent acetonitrile molecules (70-90%) are CCN and CNC radicals, which result from prompt or two-step dehydrogenation of the corresponding precursors, H2CN and CH2NC radicals, respectively. CHCN and CHNC were also found as products of dehydrogenation at high absorbed doses, whereas the fragmentation products (CH3, CN, HCN, and HNC) were detected only in minor amounts over the whole dose range studied. CCN and CNC are produced in nearly equal amounts at high absorbed doses. Selective isomerization of CCN to CNC was observed under the illumination with visible light (460-470 nm), while subsequent action of the UV light (254 nm) induced reverse transformation leading to a photostationary state with the relative population of CNC/CCN being ca. 0.7. The astrochemical implications of the obtained results are discussed in connection with the recent discovery of CCN in extraterrestrial objects.

Radiation-Induced Transformations of C6H6 Molecules in Solid Noble-Gas Matrices: Is Benzene Intrinsically Resistant in Condensed Media?

The radiation resistance of aromatic compounds is one of the key concepts of basic and applied radiation chemistry in condensed phases. Usually, it is attributed to the intrinsic radiation stability of the benzene ring. In this work, we have demonstrated for the first time that the isolated benzene molecules undergo rather efficient radiation-induced degradation in rigid inert media at cryogenic temperatures (comparable to that of aliphatic hydrocarbons), and their stability is essentially determined by the intermolecular relaxation correlating with matrix polarizability. The principal primary products of benzene radiolysis in matrices are phenyl radicals and fulvene. The matrix environment strongly affects the proportion of these species because of external heavy atom effect on the intersystem crossing, which may trigger further reaction pathways. The obtained results may have important implications for the prediction of radiation stability of complex organic systems and polymers. Furthermore, they may contribute to a better understanding of the radiation-induced evolution of aromatic species in cold interstellar media.

The HKrCCHCO2 complex: an ab initio and matrix-isolation study.

We report an experimental and theoretical study on new noble-gas hydride complex HKrCCHCO2, which is the first known complex of a krypton hydride with carbon dioxide. This species was prepared by the annealing-induced H + Kr + CCHCO2 reaction in a krypton matrix, the CCHCO2 complexes being produced by UV photolysis of propiolic acid (HCCCOOH). The H-Kr stretching mode of the HKrCCHCO2 complex at 1316 cm-1 is blue-shifted by 74 cm-1 from the most intense H-Kr stretching band of HKrCCH monomer. The observed blue shift indicates the stabilization of the H-Kr bond upon complexation, which is characteristic of complexes of noble-gas hydrides. This spectral shift is slightly larger than that of the HKrCCHC2H2 complex (+60 cm-1) and significantly larger than that of the HXeCCHCO2 complex (+32 and +6 cm-1). On the basis of comparison with ab initio computations at the MP2 and CCSD(T) levels of theory, the experimentally observed absorption is assigned to the quasi-parallel configuration of the HKrCCHCO2 complex. The calculated complexation-induced spectral shift of the H-Kr stretching band (60.4 or 72.7 cm-1 from the harmonic calculations at the MP2 and CCSD(T) levels, respectively) agrees well with the experimental value.

Matrix Isolation and Ab Initio Study on the CHF3···CO Complex.

Intermolecular complexes between CHF3 and CO have been studied by ab initio calculations and IR matrix isolation spectroscopy. The computations at the MP2 and CCSD(T) levels of theory indicated five minima on the potential energy surface (PES). The most energetically favorable structure is the C(CO)-H(CHF3) coordinated complex ( Cs symmetry) with the stabilization energy of 0.84 kcal/mol as computed at the CCSD(T) level (with ZPVE and BSSE corrections). This is the only structure experimentally found in argon and krypton matrixes, whereas the weaker non-hydrogen-bonded complexes predicted by theory were not detected. The vibrational spectrum of this complex is characterized by a red-shift of the CF3 asymmetric stretching, splitting of the C-H bending mode, and blue-shifts of the C-H and C-O stretching vibrations as compared to the monomer molecules. The observed complexation-induced shifts of CHF3 and CO fundamentals are in good agreement with the computational predictions. It was shown that both MP2 and CCSD(T) calculations generally provided a reasonable description of the vibrational properties for the weak intermolecular complexes of fluoroform.

Evidence for Indirect Action of Ionizing Radiation in 18-Crown-6 Complexes with Halogenous Salts of Strontium: Simulation of Radiation-Induced Transformations in Ionic Liquid/Crown Ether Compositions.

Ionic liquid/crown ether compositions are an attractive alternative to traditional extractants in the processes for spent nuclear fuel and liquid radioactive wastes reprocessing. These compositions are exposed to ionizing radiation, and their radiation stability, especially in the presence of metal salts, is a crucial issue. In the present study, the macrocyclic 18C6·Sr(BF4)2 and 18C6·Sr(PF6)2 complexes simulating the components of metal loaded ionic liquid/crown ether extractants were synthesized and their structures were characterized by FTIR spectroscopy and single-crystal X-ray diffraction analysis. Inclusion of Sr2+ cation into the 18C6 cavity resulted in more symmetric D3d conformations of the macrocycle. The structural transformations of the crown ether were accompanied by an elongation of polyether C-O bonds that could increase the possibility of radiolytic cleavage of the macrocycle. However, EPR study of the synthesized compounds subjected to X-ray irradiation revealed predominant formation of macrocyclic -CH2-CH-O- radicals. This result demonstrated an evidence for indirect action of ionizing radiation on individual components of the complexes and was reasonably described by a positive "hole" transfer from primary macrocyclic radical cation to fluorous anion at the primary stages of radiolysis and a subsequent interaction of fluorine atom with 18C6 macrocycle in secondary radical reactions. The observed effects may be partially responsible for enhanced sensitivity of the ionic liquid/crown ether extractants to ionizing radiation due to chemical blocking of the crown ether with radiolytic HF, radiation-chemical degradation of the 18C6, and precipitation of a low-soluble SrF2.