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1.
Phys Chem Chem Phys ; 22(25): 14155-14161, 2020 Jul 07.
Artigo em Inglês | MEDLINE | ID: mdl-32609111

RESUMO

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.

2.
J Phys Chem A ; 2020 Feb 28.
Artigo em Inglês | MEDLINE | ID: mdl-32065527

RESUMO

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.

3.
Phys Chem Chem Phys ; 21(7): 3656-3661, 2019 Feb 13.
Artigo em Inglês | MEDLINE | ID: mdl-30406252

RESUMO

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.

4.
J Phys Chem A ; 122(16): 4042-4047, 2018 Apr 26.
Artigo em Inglês | MEDLINE | ID: mdl-29627988

RESUMO

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.

5.
J Chem Phys ; 147(18): 184301, 2017 Nov 14.
Artigo em Inglês | MEDLINE | ID: mdl-29141420

RESUMO

We report on the preparation and vibrational characterization of the C2H3⋯CO2 complex, the first example of a stable intermolecular complex involving vinyl radicals. This complex was prepared in Ar and Kr matrices using UV photolysis of propiolic acid (HC3OOH) and subsequent thermal mobilization of H atoms. This preparation procedure provides vinyl radicals formed exclusively as a complex with CO2, without the presence of either CO2 or C2H3 monomers. The absorption bands corresponding to the ν5(C2H3), ν7(C2H3), ν8(C2H3), ν2(CO2), and ν3(CO2) modes of the C2H3⋯CO2 complex were detected experimentally. The calculations at the UCCSD(T)/L2a level of theory predict two structures of the C2H3⋯CO2 complex with Cs and C1 symmetries and interaction energies of -1.92 and -5.19 kJ mol-1. The harmonic vibrational frequencies of these structures were calculated at the same level of theory. The structural assignment of the experimental species is not straightforward because of rather small complexation-induced shifts and matrix-site splitting of the bands (for both complex and monomers). We conclude that the C1 structure is the most probable candidate for the experimental C2H3⋯CO2 complex based on the significant splitting of the bending vibration of CO2 and on the energetic and structural considerations.

6.
J Chem Phys ; 147(13): 131102, 2017 Oct 07.
Artigo em Inglês | MEDLINE | ID: mdl-28987105

RESUMO

Structure and spectroscopic features of the CF2⋯HF complexes were studied by ab initio calculations at the CCSD(T) level and matrix isolation FTIR spectroscopy. The calculations predict three stable structures. The most energetically favorable structure corresponds to hydrogen bonding of HF to the lone pair of the C atom (the interaction energy of 3.58 kcal/mol), whereas two less stable structures are the H⋯F bonded complexes (the interaction energies of 0.30 and 0.24 kcal/mol). The former species was unambiguously characterized by the absorptions in the FTIR spectra observed after X-ray irradiation of fluoroform in a xenon matrix at 5 K. The corresponding features appear at 3471 (H-F stretching), 1270 (C-F symmetric stretching, shoulder), 1175 (antisymmetric C-F stretching), and 630 (libration) cm-1, in agreement with the computational predictions. To our knowledge, it is the first hydrogen-bonded complex of dihalocarbene. Possible weaker manifestations of the H⋯F bonded complexes were also found in the C-F stretching region; however, their assignment is tentative. The H⋯C bonded complex is protected from reaction yielding a fluoroform molecule by a remarkably high energy barrier (23.85 kcal/mol), so it may be involved in various chemical reactions.

7.
Phys Chem Chem Phys ; 19(35): 24348-24356, 2017 Sep 13.
Artigo em Inglês | MEDLINE | ID: mdl-28849816

RESUMO

The HCNCO complex and its X-ray induced transformation to HNCCO in solid noble gas (Ng) matrices (Ng = Ne, Ar, Kr, Xe) was first characterized by matrix isolation FTIR spectroscopy at 5 K. The HCNCO complex was obtained by deposition of HCN/CO/Ng gaseous mixtures. The assignment was based on extensive quantum chemical calculations at the CCSD(T) level of theory. The calculations predicted two computationally stable structures for HCNCO and three stable structures for HNCCO. However, only the most energetically favorable linear structures corresponding to the co-ordination between the H atom of HCN (HNC) and the C atom of CO have been found experimentally. The HCNCO complex demonstrates a considerable red shift of the H-C stretching vibrations (-24 to -38 cm-1, depending on the matrix) and a blue shift of the HCN bending vibrations (+29 to +32 cm-1) with respect to that of the HCN monomer, while the C[double bond, length as m-dash]O stretching mode is blue-shifted by 15 to 20 cm-1 as compared to the CO monomer. The HNCCO complex reveals a strong red shift of the H-N bending (-77 to -118 cm-1) and a strong blue shift of the HNC bending mode (ca. +100 cm-1) as compared to the HNC monomer, whereas the C[double bond, length as m-dash]O stretching is blue-shifted by 24 to 29 cm-1 with respect to that of the CO monomer. The interaction energies were determined to be 1.01 and 1.87 kcal mol-1 for HCNCO and HNCCO, respectively. It was found that the formation of complexes with CO had a remarkable effect on the radiation-induced transformations of HCN. While the dissociation of HCN to H and CN is suppressed in complexes, the isomerization of HCN to HNC is strongly catalyzed by the complexation with CO. The astrochemical implications of the results are discussed.

8.
Artigo em Inglês | MEDLINE | ID: mdl-28646663

RESUMO

Formyl radical HCO is an important reactive intermediate in combustion, atmospheric and extraterrestrial chemistry. Like in the case of other transients, the lack of knowledge of the absolute IR intensities limits the quantitative spectroscopic studies on this species. We report the first experimental determination of the absorption intensities for the fundamental vibrational bands of HCO. The measurements have been performed using matrix-isolation FTIR spectroscopy. Determination of the values was based on the repeated photodissociation and thermal recovery of the HCO radical using the known value of the absorption coefficient of CO. The experimentally determined values (93.2±6.0, 67.2±4.5, and 109.2±6.6kmmol-1 for the ν1, ν2, and ν3 modes, respectively) have been compared to the calculated IR intensities obtained by DFT and UCCSD(T) computations.

9.
J Phys Chem A ; 120(40): 7847-7858, 2016 Oct 13.
Artigo em Inglês | MEDLINE | ID: mdl-27643620

RESUMO

The X-ray-induced transformations of simple chlorofluorocarbons (CFCl3 and CF2Cl2) in solid noble-gas matrixes (Ne, Ar, Kr, and Xe) at 7 K were studied in order to elucidate basic mechanisms of the radiation-chemical degradation with possible implications for stratospheric and extraterrestrial ice chemistry. The decomposition of parent molecules and formation of products were monitored by FTIR spectroscopy, and the identification was supported by ab initio calculations at the CCSD(T) level. It was shown that the ionic reaction channels were predominating in most cases (except for CF2Cl2/Xe system). The primary radical cations (CFCl3+• and CF2Cl2+•) are either stabilized in matrixes or undergo fragmentation to yield the corresponding secondary cations (CFCl2+, CCl3+, CF2Cl+) and halogen atoms. The probability of fragmentation through different channels demonstrates a remarkable matrix dependence, which was explained by the effect of excess energy resulting from the exothermic positive hole transfer from matrix atoms to freon molecules. A qualitative correlation between "hot" ionic fragmentation at low temperatures and gas-phase ion energetics was found. However, dissociative electron attachment leads to formation of neutral radicals (CFCl2• or CF2Cl•) and chloride anions. One more possible way of dissociative electron attachment in the case of CF2Cl2 is formation of CF2•• and Cl2-•. A general scheme of the radiation-induced processes is proposed.

10.
J Chem Phys ; 145(21): 214309, 2016 Dec 07.
Artigo em Inglês | MEDLINE | ID: mdl-28799372

RESUMO

Spectroscopic characteristics and X-ray induced transformations of the HCN⋯CO2 complex in solid Ar and Kr matrices were studied by FTIR spectroscopy and ab initio calculations at the CCSD(T) level. The complex was prepared by deposition of the HCN/CO2/Ng gas mixtures (Ng = Ar or Kr). The comparison of the experiment and calculations prove formation of a linear, H-bonded NCH⋯OCO complex with a substantial red shift of the C-H stretching band and a blue shift of the H-C-N bending band in respect to the monomer. This result is in contrast with the previous gas-phase observations, where only T-shape complex was found. Irradiation of deposited matrices leads to formation of CN radicals and HNC molecules and subsequent annealing results in appearance of H2CN and trans-HCNH in both matrices plus HKrCN in the case of Kr. In the presence of CO2, the strongest absorption of trans-HCNH radical demonstrates an additional blue-shifted (by 6.4 cm-1) feature, which was assigned to the N-coordinated complex of this radical with CO2 on the basis of comparison with calculations. To our knowledge, it is the first experimentally observed complex of this radical. No evidence was found for HKrCN⋯CO2 complex, which was explained tentatively by steric hindrance.

11.
Phys Chem Chem Phys ; 12(31): 8863-9, 2010 Aug 21.
Artigo em Inglês | MEDLINE | ID: mdl-20535405

RESUMO

The EPR spectrum of the Y@C(82) molecules isolated in solid argon matrix was recorded for the first time at a temperature of 5 K. The isotropic hyperfine coupling constant (hfcc) A(iso) = 0.12 +/- 0.02 mT on the nucleus (89)Y as derived from the EPR spectrum is found in more than two times greater than that obtained in previous EPR measurements in liquid solutions. Comparison of the measured hfcc on a metal atom with that predicted by density-functional theory calculations (PBE/L22) indicate that relativistic method provides good agreement between experiment in solid argon and theory. Analysis of the DFT calculated dipole-dipole hf-interaction tensor and electron spin distribution in the endometallofullerenes with encaged group 3 metal atoms Sc, Y and La has been performed. It shows that spin density on the scandium atom represents the Sc d(yz) orbital lying in the symmetry plane of the C(2v) fullerene isomer and interacting with two carbon atoms located in the para-position on the fullerene hexagon. In contrast, the configuration of electron spin density on the heavier atoms, Y and La, is associated with the hybridized orbital formed by interaction of the metal d(yz) and p(y) electronic orbitals.

12.
Inorg Chem ; 48(18): 8723-8, 2009 Sep 21.
Artigo em Inglês | MEDLINE | ID: mdl-19694454

RESUMO

Xenon trifluoride radicals were generated by the solid-state chemical reaction of mobile fluorine atoms with XeF(2) molecules isolated in a solid argon matrix. On the basis of spectroscopic and kinetic FTIR measurements and performed quantum chemical calculations, two infrared absorption bands at 568 (strong) and 523 (very weak) cm(-1) have been assigned to asymmetric and symmetric Xe-F stretching vibrational modes of radical (*)XeF(3), respectively. Chemical reaction of fluorine atom with XeF(2) in a solid argon cage obeys specific kinetic behavior indicating the formation of a long-lived intermediate complex under the condition that the diffusing fluorine atom is attached to isolated XeF(2) at temperatures 20 K < T < 27 K. Subsequent thermally activated conversion in the complex is the main source of novel xenon-containing radical species (*)XeF(3). The rate constant and energy barrier are estimated for the reaction in an argon cage, [XeF(2)-F] --> (K(r)) [XeF(3)], as K(r) approximately 7 x 10(-5) c(-1) at 27 K and E approximately 1.2 kcal/mol, respectively. Quantum chemistry calculations reveal that radical (*)XeF(3) has a planar C(2v) structure. DFT calculations show that formation of the third Xe-F bond in the (*)XeF(3) radical is exothermic, and the binding energy of the third Xe-F bond is 8-20 kcal/mol.

13.
J Chem Phys ; 123(6): 64318, 2005 Aug 08.
Artigo em Inglês | MEDLINE | ID: mdl-16122319

RESUMO

Vinyl radicals produced by annealing-induced reaction of mobilized hydrogen atoms with acetylene molecules in solid noble-gas matrices (Ar, Kr, and Xe) were characterized by Fourier transform infrared and electron paramagnetic resonance (EPR) spectroscopies. The hydrogen atoms were generated from acetylene by UV photolysis or fast electron irradiation. Two vibrational modes of the vinyl radical (nu7 and nu5) were assigned in IR absorption studies. The assignment is based on data for various isotopic substitutions (D and 13C) and confirmed by comparison with the EPR measurements and density-functional theory calculations. The data on the nu7 mode is in agreement with previous experimental and theoretical results whereas the nu5 frequency agrees well with the computational data but conflicts with the gas-phase IR emission results.

14.
J Phys Chem A ; 109(28): 6166-73, 2005 Jul 21.
Artigo em Inglês | MEDLINE | ID: mdl-16833956

RESUMO

The radical cations of piperazine, morpholine, thiomorpholine, and thioxane were investigated by electron paramagnetic resonance (EPR) and electron-nuclear double resonance (ENDOR) spectroscopy in a solid Freon matrix. Optimized geometry and magnetic parameters of the radical cations were calculated using a density functional theory (DFT)/Perdew-Burke-Ernzerhof (PBE) method. Both experimental and theoretical results suggest that all the studied species adopt chair (or distorted chair) conformations. No evidence for the boat conformers with intramolecular sigma-bonding between heteroatoms were obtained. In the cases of morpholine and thioxane, the oxygen atoms are characterized by relatively small spin populations, whereas a major part of spin density is located at N and S atoms, respectively. The thiomorpholine radical cation exhibits nearly equal spin population of N and S atoms. In most cases (except for thioxane), the calculated magnetic parameters agree with the experimental data reasonably well.

15.
Inorg Chem ; 41(23): 6147-52, 2002 Nov 18.
Artigo em Inglês | MEDLINE | ID: mdl-12425645

RESUMO

Syntheses of title compounds, viz. N(CH2CH2NR)3E (1, E = Sb, R = Me; 4, E = Bi, R = Me; 6, E = Sb, R = SiMe3; 8, E = Bi, R = SiMe3), by the reaction of E(NAlk2)3 (3, E = Sb, Alk = Et; 5, E = Bi, Alk = Me) with N(CH2CH2NMeH)3 (2) or N(CH2CH2NSiMe3H)3 (7) are reported. The reactions of SbCl3 with N[CH2CH2N(Me)Li]3 or N[CH2CH2N(SiMe3)Li]3 and BiCl3 with N[CH2CH2N(SiMe3)Li]3 resulted in compounds 1, 6, and 8, respectively. Composition and structures of all novel compounds were established by 1H and 13C NMR spectroscopy and mass spectrometry. The X-ray structural study of 8 clearly indicated the presence of transannular interaction BiNdat in this compound, while 6 possesses a long Sb...Ndat distance. The structural data obtained from geometry optimizations on 6 and 8 reproduce experimental trends, i.e., a decrease in the E-Ndat distance from Sb to Bi. The values of electron density in E-Ndat critical point and the Laplacian of charge density for 8 indicate that a closed-shell interaction exists between the metal atom and Ndat atom.

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