Far IR and Raman vibrational spectra of nitramines

Vibrational spectra of several nitramines in the long-wave region (50–450 cm⁻¹) were studied. The frequencies of intra- and intermolecular vibrations were separated and a tentative assignment of the frequencies of self-associative complexes was performed. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 11, pp. 2241–2244, November, 1998.     

Features in the vibrational relaxation of laser excited Freon-22 molecules

The vibration-translation (V-T) of laser excited Freon-22 (CF₂HC1) molecules has been studied. An interferometric technique allows simultaneous measurement of the initial energy 〈E〉 stored in the molecules, and of the V-T relaxation time. Consequently, the V-T relaxation time and the energy released per collision can be determined as a function of the energy absorbed from the laser field. Three distinct regions have been observed for these dependences. This behaviour observed and reported by us for Freon-22 confirms the role played in the relaxation process by the initial distribution of the vibrational energy, and agrees qualitatively with the experimental results for other polyatomic molecules.     

Laser-induced fluorescence study of the hydrogen atom formation dynamics in the 248 nm gas-phase photodissociation of vibrational state selected water (H<Subscript>2</Subscript>O (|04<Superscript>−</Superscript>〉))

The vibrationally-mediated H₂O gas-phase photodissociation was studied at a photolysis wavelength of 248 nm. Single rotational states of the |03⁻〉|2〉 and |04⁻〉 H₂O overtone vibrations were prepared by laser photoexcitation around 720 nm. H atoms formed in the photodissociation of the H₂O (|04⁻〉 = 3₁₃) were detected by Lyman-α laser-induced fluorescence spectroscopy with sub-Doppler resolution to determine their translational energy. The present result confirms that in the dissociation process the major part (ca. 93%) of the available energy is released as relative translational energy of the nascent H + OH photofragments, in agreement with earlier complementary measurements (R. L. Vander Wal, J. L. Scott and F. F. Crim, J. Chem. Phys. 94, 1859 (1991)), where the internal excitation of the OH product radical was investigated at different photolysis wavelengths.     

Theoretical studies on the potential energy surfaces and vibrational energy levels of HXeF and HXeCl

The potential energy surfaces for the electronic ground state of the HXeCl and HXeF molecules areconstructed by using the internally contracted multi-reference configuration interaction with theDavidson correction(icMRCI Q)method and large basis sets.The stabilities and dissociation barriersare identified from the potential energy surfaces.The three-body dissociation channel is found to bethe dominate dissociation channel for HXeCl,while two dissociation channels are possible and com-petitive for HXeF.Based on the obtained potentials,vibrational energy levels of HXeCl and HXeF arecalculated using the Lanczos algorithm.Our theoretical results are in good agreement with the avail-able observed values.Particularly,the calculated fundamental frequency of the H—Xe stretching vi-bration including the Xe matrix effect of HXeCl is found to be 1666.6 cm-1,which is only 17.6 cm-1higher than the recently observed value of 1649 cm-1.     

Vibrational spectra of 1,1,3,3-tetramethyl-2-nitroguanidine and their interpretation with the use of scaling of quantum-chemical force field

The IR (4000–50 cm⁻¹) and Raman (3500–170 cm⁻¹) spectra of solid 1,1,3,3-tetramethyl-2-nitroguanidine (TMNG) were obtained. The spectra were interpreted using the scaling of the TMNG quantum-chemical force field in the B3LYP/6-311G(d,p) approximation. Transferable scale factors necessary for the interpretation of spectra of more complex related compounds were determined. The scaled harmonic force field is supposed to be used in the analysis of the available gas-phase electron diffraction data for TMNG. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 3, pp. 495–498, March, 2008.     

Mechanism of vibrational relaxation and intersystem crossing within excited ion-pair states of I2

Visible and ultraviolet fluorescence of I₂, following excitation by ArF/193nm excimer laser pulses, was recorded for different pressures of argon buffer gas in a flow system. Dispersed fluorescence spectra due to the transitionsD’(2_g) → A’(2_y andD(0 _n ⁺ )→X0 _g ⁺ ) were analysed by inversion and spectral simulations. Thus vibrational distributions in the emitting states were obtained as a function of pressure to determine the mechanism of relaxation to populate the lowest quantum levels of theD’ state, which are the emitting states in the iodine laser. Fast intersystem crossing is found to occur from initially populated vibrational levels of theD state to other ion-pair states correlating with the ground state ions, followed by rapid relaxation, involving both direct vibrational relaxation within individual states and intersystem crossing between states.     

Vibrational spectroscopy of silver perchlorate and silver trifluoromethanesulfonate solutions in acrylonitrile

Solutions of silver trifluoromethanesulfonate (“triflate”) and silver perchlorate in acrylonitrile, over a range of concentrations between 0.5 and 4 mol.kg^-1 have been analyzed by dispersive infrared and Fourier-transform Raman spectroscopy. The spectral regions studied include the solvent v(C≡N) fundamental and several anion internal modes. The silver ion solvation number in the infinite dilution limit is 3 in both systems. This number falls when the salt concentration is increased because of the ionic pairing, which is slightly more intense for silver perchlorate solutions, with a calculated spectroscopic association constant 0.23 ±0.08 kg-mol^-1. For silver triflate solutions, the spectroscopic association constant is 0.17±0.05 kg-mol^-1. In both cases, the ionic pair structure is bidentate and silver ion preserves two molecules of acrylonitrile in its first solvation shell.     

Structure effects on isomerization pathways and vibrational spectra of epoxysaccharides: a numerical study

Results of a comparative analysis of conformational possibilities of the hexopyranose ring of six epoxysaccharides differing from each other by the position of the oxirane ring within the limits of the hexapyranose ring and having different orientations of substituents and different positions of the oxirane ring with respect to the skeleton plane of the molecules are presented. Numerical simulations based on the Wiberg and Boyd method made it possible to determine all the stationary forms in which anhydropyranose rings can exist. The effect of various structural factors on the character of conformational transformations, heights of transition barriers, and the energy of stationary forms has been investigated. Normal vibrational modes of the stationary forms of the compounds were calculated using molecular mechanics. Based on results of our simulations, we predict a strong effect of steric factors on the vibrational spectra of sugar epoxides. Received: 24 March 1998 / Accepted: 3 September 1998 / Published online: 17 December 1998     

A numerical study of time-dependent schr?dinger equation for multiphoton vibrational interaction of NO molecule, modelled as Morse oscillator, with intense far-infrared femtosecond lasers

For the NO molecule, modelled as a Morse oscillator, time-dependent (TD) nuclear Schr?dinger equation has been numerically solved for the multiphoton vibrational dynamics of the molecule under a far-infrared laser of wavelength 10503 nm, and four different intensities,I = 1 × 10⁸, 1 × 10¹³, 5 × 10¹⁶, and 5 × 10¹⁸ W cm⁻² respectively. Starting from the vibrational ground state at zero time, various TD quantities such as the norm, dissociation probability, potential energy curve and dipole moment are examined. Rich high-harmonics generation (HHG) spectra and above-threshold dissociation (ATD) spectra, due to the multiphoton interaction of vibrational motions with the laser field, and consequent elevation to the vibrational continuum, have been obtained and analysed. Dedicated to Professor C N R Rao on his 70th birthday An erratum to this article is available at .     

Inversion of ν(MHal) stretching frequencies in the spectra of dihalosilylenes, -germylenes, -stannylenes,and their complexes with Lewis bases

The vibrational spectra of tetravalent metal halides (M = Si, Ge, Sn) and the corresponding dihalocarbene analogs M^IIHal₂, obtained by the authors, and the relevant published data are compared. The spectra of the M^IIHal₂ species exhibit inversion of the M-Hal stretching frequencies (ν^s(M^IIHal) > ν ^as(M^IIHal)). This can be used for analytical purposes and allows one to distinguish between the spectra of the M^IV and M^II halides. The IR and Raman spectra of the complexes of dihalogermylenes and -stannylenes with triphenylphosphine and 1,4-dioxane also exhibit inversion of the ν(MHal) stretching frequencies. This confirms the conclusion drawn earlier based on the analysis of the geometric parameters and reactivities of the complexes in question that the divalent state of the M atom in these species is retained. Dedicated to Academician N. K. Kochetkov on the occasion of his 90th birthday. __________ Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 5, pp. 1089–1092, May, 2005.     

Concerning the problem of temperature changes in the intensity of continuous absorption in the spectra of complexes with symmetric H-bond

The effect of temperature on the spectra of anharmonic vibrations of complexes with symmetric H-bonds was simulated and considered using H₃O₂ ⁻ and H₅O₂ ⁺ ions as an example. The intensity of continuous absorption observed in the IR spectra of such types of complexes is virtually independent of temperature. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 8, pp. 1447–1449, August, 1997.     

Raman spectra and molecular dynamics of R2NPX2 (R=Me and Et; X=F, Cl, and Br)

The Raman spectra of compounds R₂NPX₂ (R=Me and Et; X=F, Cl, and Br) were studied. The time correlation functions of vibrational and rotational relaxations as well as the characteristic times of these processes were calculated. Conclusions concerning the mechanisms of formation of the contours of the Raman lines with frequencies in the 670–705 cm⁻¹ range corresponding to the totally symmetric vibrations of the P-N bond in the R₂NPX₂ molecules were drawan. Translated fromIzvestiya Akademii Nauk, Seriya Khimicheskaya, No. 5, pp. 961–967, May 1997.     

Structural and vibrational theoretical analysis of protonated formaldehyde in its $$\tilde{X}^{1} A^{\prime}$$ ground electronic state

A structural and vibrational study of protonated formaldehyde (H₂COH⁺) in its ground electronic state, at the CCSD/cc-pVTZ theory level, is presented. The variation of the molecular structure with the torsion angle shows clear dependence of the H₂C wagging and COH angles. Anharmonic one- and two-dimensional vibrational models for two out-of-plane vibrational modes (H₂C torsion, and H₂C wagging) are constructed. Since H₂COH⁺ is classified under a G₄ non-rigid group, the vibrational Hamiltonians are factorized using the symmetry of the G₄ group and solved variationally. The one-dimensional results for torsion and wagging yield fundamental frequencies are 844.12 and 1,252.89 cm⁻¹, respectively. A two-dimensional COH angle + torsion model gives a torsion frequency of 762.32 cm⁻¹. Finally, a wagging + torsion model predicts frequencies of 931.93 and 1,255.82 cm⁻¹ for torsion and wagging, respectively. The variation of frequency values for torsion suggests an important coupling between this mode and the bending and wagging vibration modes.     

Vibrational spectra of volatile inorganic hydrides in the liquid state

The results of studies of IR and Raman spectra of volatile inorganic hydrides of Group IV–VI and Periods 3 and 4 elements in the liquid state are surveyed and analyzed. The mechanisms of intermolecular interactions in these liquids are discussed. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 4, pp. 629–644, April, 1999.     

Ab initio study of molecular structure and internal rotation in methyldicyanophosphine and methyldiisocyanophosphine. The Raman spectrum of methyldicyanophosphine and its interpretation with the use of scaling ofab initio force fields

The equilibrium geometric parameters and structures of transition states of internal rotation for the molecules of methyldicyanophospine MeP(CN)₂ and its isocyano analog MeP(NC)₂ were calculated by the RHF and MP2 methods with the 6–31G^* and 6–31G^** basis sets. At the MP2 level, the total energy of cyanide is −35 kcal mol⁻¹ lower than that of isocyanide and the barriers to internal rotation of methyl group for MeP(CN)₂ and MeP(NC)₂ are 2.2 and 2.7 kcal mol⁻¹, respectively. For both molecules, the one-dimensionalab initio potential functions of internal rotation approximated by a truncated Fourier series were used to determine the frequencies of torsional transitions by solving direct vibrational problems for a non-rigid model. The Raman spectrum of crystalline MeP(CN)₂ was recorded in the range 3500–50 cm⁻¹. The vibrational spectra of this compound were interpreted by scalingab initio force fields calculated by the RHF and MP2 method. The vibrational spectrum of methyldiisocyanophosphine was predicted with the use of the obtained scale factors. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 9, pp. 1703–1714, September, 1998.     

Theoretical study on the vibrational state distribution of product CO in the photolysis of acetoneCH_3 COCH_3 \underrightarrow {hv}2CH_3 + CO

The photolysis of acetone has been studied at 6-311G basis set using unrestricted Hartree-Fock method. The results show that ground state acetone (S_o) cannot easily dissociate. The electrons of acetone undergo n→II transition in laser, and excited acetone (T₁) can easily dissociate: and acetyl can further undergo themolytic dissociation: CH₃CO→CH₃+CO(R₂). The dynamic information (ω_k B _KF V₀(S)) of reaction R₂ is obtained and the vibrational state distributions of product CO are calculated. The calculated value consists with the experimental value. Project supported by the National Natural Science Foundation of China (Grant No. 29773007).     

A theoretical study on the first ionic states of vinyl fluoride, vinyl chloride, trifluoroethylene, and trichloroethylene with an analysis of the vibrational structures of the photoelectron spectra

Ab initio calculations have been performed to study the molecular structures and the vibrational levels of the first ionic states of vinyl fluoride, vinyl chloride, trifluoroethylene, and trichloroethylene. The equilibrium molecular structures and vibrational modes of these states are presented. The theoretical ionization intensity curves including the vibrational structures are also presented and compared with the photoelectron spectra. Received: 11 September 1998 / Accepted: 13 October 1998 / Published online: 1 February 1999     

Improvement of the standard method for solving the problem of internal rotation in molecules with symmetrical tops

Drawbacks of the standard method for solving the problem of internal rotation (IR) in molecules with symmetrical tops were examined. The drawbacks can be eliminated by taking into account the higher harmonics of the IR potentials. A new calculation procedure based on the approximation of the lower portion of the potential curve by the equationV(φ)=1/2V _n ^* (1-cosn φ), which describes adequately the arrangement of the torsion levels, was proposed. The successfull implementation of the proposed procedure showed that the procedures used currently are incorrect as well as the Herschbach procedure, which includes a systematic error at each iteration step. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 2, pp. 239–244, February, 1999.     

Computation of Heat Capacities of Solids Using a General Tarasov Equation

The general Tarasov function is fitted to the skeletal heat capacities of materials with widely different crystal structures. Examples are chosen from flexible macromolecules (polyethylene, polypropylene, poly(ethylene terephthalate), selenium, rigid macromolecules (diamond and graphite), and a small molecule (fullerene, C60). A new optimization approach using the MathematicaTM software is developed. It results in one-, two-, and three-dimensional Debye temperatures, Θ1, Θ2 and Θ3 the fitting parameters of the Tarasov function. In addition to the Tarasov function, the evaluation of the heat capacities makes use of approximate group-vibrational spectra. The results support the earlier assumption that Θ2=Θ3 for simple, solid, linear macromolecules. In more complicated bonding situations, Θ1, Θ2 and Θ3 are used as averaging fitting parameters. This general approach provides an improvement in the quantitative thermal analyses of polymers and other substances included in the ATHAS Data Bank. Sufficient programming information is provided to enable anyone the computation with a copy of the popular MathematicaTM software. The programming file is also downloadable from the WWW. This revised version was published online in July 2006 with corrections to the Cover Date.