George Pitsevich

Belarusian State University | BSU · Department of Physical Optics

Splitting of the ground state and some excited symmetric bending vibrational states due to inversion tunneling of the oxygen atom in the H3O+, H3O- ions and in the H3O radical are analyzed by numerically solving the vibrational Schrödinger equation of restricted (2D) dimensionality. As two vibrational coordinates, we used 1) the distance of the oxy...

Torsional vibrations of free and hydrogen-bonded hydroxyl groups of the 1,2-dihydroxybenzene molecule are analyzed within the harmonic and anharmonic approximations, as well as by constructing a 2D potential energy surface formed by varying the torsional coordinates of the two O–H groups. Calculation of the vibrational spectrum of the molecule in t...

Compound synthesized N-[4-((2R)-octan-2-yloxy)benzyl]-N,N-dimethyl-hexadecane-1-aminium tosylate, which is a promising candidate for use in liquid crystal compositions. The Raman spectrum of the synthesized sample was also recorded. The equilibrium configuration of the molecule (ion) was calculated by optimization for all geometric parameters at th...

Geometric parameters of equilibrium configurations of trans- and cis-conformers of HSOSH molecule, their dipole moments, rotational constants in the ground electronic and vibrational states, and kinetic parameters corresponding to two torsional coordinates γ1 and γ2 were calculated at CCSD(T)-F12/cc-pVDZ-F12 level of theory. In the latter case, at...

The 2D surfaces of potential energy, kinematic coefficients, components of the dipole moment, the heights of potential barriers, the energies of stationary torsional states, and the tunneling frequencies of hydroxyl and methyl groups in the methyl hydroperoxide molecule were calculated at MP2/CBS and CCSD(T)/Aug-cc-pVTZ levels of theory. Additional...

2D surfaces of potential energy, dipole moment, and kinetic coefficients associated with internal rotation of the thiol groups in the HSOSH molecule were calculated and analyzed at MP2/CBS level of theory. Two stable conformers (trans- and cis-) with very close energies were found. Torsional vibrations of the HSOSH, DSOSH, and DSOSD molecules were...

Torsional vibrations of sulfoxylic acid molecule (HOSOH) and its two deuterated isotopologues were analyzed for the first time. Harmonic and anharmonic calculations of the vibrational frequencies of the trans- and cis- conformers were performed. More rigorous consideration of the torsional vibrations was made based on 2D (two-dimensional) potential...

Torsional states caused by vibrations of hydroxyl groups in the methanediol molecule and its two deuterated analogues – DO(CH2)OH and DO(CH2)OD were analysed at MP2/cc-pVTZ and CCSD(T)/cc-pVQZ levels of theory. In the first case, 2D PES and 2D surfaces of kinematic coefficients were calculated with geometry optimisation for all other geometric para...

The hydrogen trioxide (HT) molecule HOOOH is (1) a prototype for a class of molecules of the form X(ZY)2 with two equivalent internal tops (ZY) and (2) the second representative of the polyoxides series of the form HOnH (n ≥ 2). Due to this, it is the subject of close attention of researchers. In this paper, we performed a group theory analysis of...

Structure and spectral characteristics of eight compounds with hydrogen bonds of different strength were calculated at the B3LYP/cc-pVTZ level of theory. A wide range of variation of the hydrogen bond strength in the analyzed compounds allowed us to obtain correlation dependences between the structural characteristics of the hydrogen bridge, the ca...

The energies of the stationary torsional levels of the hydrogen trioxide molecule were calculated at the B3LYP, MP2, and CCSD(T) levels of theory using augmented correlation consistent acc-pVTZ basis set. The molecular symmetry group whose elements are inherent to both equilibrium conformer's symmetry elements (C2 and CS) of the HT molecule was fou...

Based on recent experimental data that can be interpreted as indicating the presence of specific structures in liquid water, we build and optimize two structural models which we compare with the available experimental data. To represent the proposed high-density liquid structures, we use a model consisting of chains of water molecules, and for low-...

Internal rotation of two of hydroxyl groups in a methanediol molecule is analyzed by constructing the 2D surfaces of the potential energy, kinematic coefficients and dipole moment. The molecular characteristics in the nodes of 2D grids with different densities for distinct pairs of dihedral angles of O-H groups were calculated at the MP2/cc-pVQZ le...

Different configurations of (H5O2)⁺− Ar, (H5O2)⁺− Ne and (H5O2)⁺− He complexes were calculated using DFT methods and series of Dunning and Pople basis sets. The possibility of the existence of an equilibrium configuration with C2 symmetry for complexes analyzed was in focus of the studies carried out. DFT methods that do not take into account dispe...

Effects of the dispersion interactions on the parameters of the water dimer equilibrium configuration and IR spectra are analyzed in the paper. Dimer equilibrium geometry was calculated using a series of the density functionals, both with (B3LYP-D3, B2PLYPD, B2PLYP-D3, mPW2PLYPD, wB97XD) and without (B3LYP, B2PLYP, mPW2PLYP, wB97X) accounting of th...

Raman spectra of liquid water and ice were measured at different temperatures. The intensity of the band assigned to bending vibrations of water molecules was observed to decrease at the liquid-to-solid transition, while the Raman line near 2200cm-1showed an anomalously high intensity in the solid phase. A tetrahedral model was used for computer an...

Previously calculated multidimensional potential-energy surfaces of the MeOH monomer and dimer, water dimer, malonaldehyde, formic acid dimer, free pyridine-N-oxide/trichloroacetic acid complex, and protonated water dimer were analyzed. The corresponding harmonic potential-energy surfaces near the global minima were constructed for series of cluste...

IR absorption spectra of methanol trapped in a nitrogen matrix were registered at different temperatures from 9 to 34 K. Changes occurring during matrix temperature increasing has been analyzed. Using quantum chemical calculations of geometry and spectral parameters of different methanol clusters an assignment of the observed absorption bands was m...

IR absorption spectra of methanol isolated in a nitrogen matrix are recorded at temperatures ranging from 9 to 34 K. The changes in the spectra with increasing matrix temperature are analyzed. Based on quantum-chemical calculations of the geometric and spectral parameters of different methanol clusters, the observed absorption bands are identified....

The frequencies and intensities of vibration–rotational transitions of water molecules in an argon matrix were calculated for temperatures of 6 and 30 K. The rigid asymmetric top approximation was used with available literature values of the effective rotational constants in the ground and excited vibrational states. The calculations were carried o...

The structure and frequencies of the protonated water dimer normal vibrations were calculated at the MP4/Aug-cc-pVTZ level of theory. Shared proton stretching vibrations were analyzed by constructing 4D potential energy surface using normal coordinates , which describe intermolecular vibration of water monomers, stretching and bending vibrations of...

The structure and harmonic- and anharmonic IR spectra of the protonated water dimer (PWD) were calculated in C1, C2 and CS symmetry at the MP4/acc-pVTZ level of theory. We found that structure and IR spectra are practically identical in C2 and C1 symmetry demonstrating that an equilibrium С1 configuration of the PWD is not realized. Anharmonic coup...

The potential energy curves of the low-lying electronic states correlating up to the limit K(4p) + Rb(5s) of KRb molecule have been calculated using the multi-reference perturbation theory method at the CASSCF/ XMCQDPT2 level of theory without and with spin–orbit coupling. The calculated parameters of the ground X 1 R + state are in the best agreem...

A new mechanism for combinatorial broadening of donor-OH stretching-vibration absorption bands in molecular clusters with H-bonds is proposed. It enables the experimentally observed increase of the O–H stretching-vibration bandwidth with increasing number of molecules in H-bonded clusters to be explained. Knowledge of the half-width of the OH stret...

The structure and the medium effects exerted on the spectral characteristics of the carbonyl group stretching vibrations in some structural fragments of poly-3-hydroxybutyrate have been analyzed. Calculations of the equilibrium configurations and IR spectra were carried out using the Gaussian program set in the approximation B3LYP/cc-pVDZ. It has b...

A hybrid method for analyzing vibrations of molecules and complexes with potential energy surface (PES), which is characterized by a high degree of anharmonicity, is proposed in the present book. A special feature of the method is the accounting of all vibrational degrees of freedom. Here the full set of vibrational coordinates is divided into two...

Using two sets of effective rotational constants for the ground (000) and the excited bending (010) vibrational states the calculation of frequencies and intensities of vibration-rotational transitions for J(″)=0-2; and J(')=0-3; was carried out in frame of the model of a rigid asymmetric top for temperatures from 0 to 40K. The calculation of the i...

Results of numerical solutions of multi-dimensional Schrödinger equations by Fourier and discrete-variable-representation (DVR) methods were compared. Both methods showed comparable accuracy in cases with a smooth potential-energy surface (PES) such as the harmonic 2D PES associated with C=O stretching vibrations in CO2 and the 3D PES associated wi...

Geometrical parameters and vibrational spectra of trans and gauche conformers of the ethanol molecules were calculated using B3LYP/cc-pVQZ and B3LYP/acc-pVQZ approximations. 2D potential energy surfaces for the internal rotation of the hydroxyl and methyl tops were built. Kinetic parameters associated with torsion coordinates were calculated using...

The structure and IR absorption spectrum of the formic acid dimer (FAD) were calculated using the B3LYP DFT functional and cc-pVTZ basis set. Matrices of force and anharmonic constants were calculated in order to find the fundamental frequencies more accurately. The 1D and 2D potential energy surfaces (PES) were built using symmetry coordinates and...

Force fields, anharmonic constant matrices, and harmonic and anharmonic frequencies of vibrational states of BF3 and BH3 were calculated using B3LYP/cc-pVTZ/cc-pVQZ/cc-pV5Z/acc-pV5Z approximations. Anharmonic IR spectra of the molecules were calculated by the vibrational self-consistent field (VSCF) method included in the quantum chemistry package...

IR and Raman spectra of the malonaldehyde molecule and its deuterated analogues were calculated in the B3LYP/cc-pVQZ approximation. Anharmonicity effects were taken into account both in the context of a standard model of the second order perturbation theory and by constructing the potential energy surfaces (PES) with a limited number of dimensions...

FTIR spectra of 1-propanol in an argon matrix were studied in the range 11–30 K. Principal component analysis of dynamic FTIR spectra and nonlinear band shape fitting has been carried out. The peaks of monomer, open dimer, mixed propanol-water dimer and those of higher H-bond clusters have been resolved and analyzed. The attribution of certain FTIR...

The analysis of O-H...O stretching vibrations of the pyridine N-oxide/trichloroacetic acid (PyO/TCA) H-bond complex in acetonitrile solution was carried out. 1D and 2D potential energy surfaces associated with the variation of valence coordinates of hydroxyl and hydrogen bonds were calculated for this purpose in the B3LYP/cc-pVTZ approximation. The...

Long-wave Raman spectra of some normal alcohols (from n-pentanol to n-decanol) in the liquid phase were registered. The regularities in the dependencies of Raman bands frequencies on the number of carbon atoms in the hydrocarbon chain were deduced. The calculations of Raman spectra of the studied molecules, their equilibrium structures and possible...

FTIR spectra of pyridine N-oxide and trichloroacetic acid H-bonded complex in acetonitrile were studied at 20 and 50°C. The calculations of equilibrium configurations of the complex and their IR spectra in harmonic- and anharmonic approximations were carried out at the level of B3LYP/cc-pVTZ/PCM. However both approximations turned out to be incompe...

Low-temperature infrared absorption spectra are obtained for ethanol isolated in an argon matrix at temperatures of 20–45 K range for ratios of the numbers of the molecules being studied to the numbers of matrix atoms of 1:1000 and 1:2000. A preliminary interpretation of the spectra is obtained on the basis of the temperature variations in the spec...

The geometry optimization for the pyridine N-oxide/trichloroacetic acid complex is realized in B3LYP/cc-pVTZ approximation. Computations of IR absorption spectra for the optimized configuration are performed in harmonic and anharmonic approximations. It is found that taking into account the anharmonicity effects leads to the red shift of the stretc...

A simple approach to the formation of a Hamiltonian matrix for some Schrödinger equations describing the molecules with large amplitude motions has been proposed. The algorithm involving one or several variables has been concretely defined for the basis functions represented by Fourier series and orthogonal polynomials, taking Hermitian polynomials...

Low-temperature FTIR spectra of ethanol in the argon matrix have been recorded in the spectral interval 2800-4000 cm-1. The spectra were obtained for several temperatures over the range 20-50 К and for the number ratios 1:1000 and 1:2000 of the mo lecules studied and atoms in the matrix. A tentative interpretation has been performed on the basis of...

The force field of a benzene molecule computed using the quantum-chemical GAMESS package with a set of independent vibrational coordinates in the approximation B3LYP/cc-pVTZ has been transformed to the set of redundant vibrational coordinates including all groups of the equivalent natural coordinates. It has been demonstrated that by the use of the...

In the approximation B3LYP/cc-pVTZ, the geometry of a methanol molecule surrounded by eight argon atoms has been optimized. Using a fixed configuration of argon atoms, the internal rotation barriers of methyl and hydroxyl groups, the values of which are compared with that for a free molecule, have been computed. It has been found that insignificant...

In the approximation B3LYP/cc-pVTZ, the geometry of a methanol molecule surrounded by eight argon atoms has been optimized. By the independent rotation of the methyl and the hydroxyl groups at the fixed position of the C-O bond relative to the argon atoms there was obtained the two-dimensional grid of values of the internal-overall rotation energy....

The valence force fields of methane and methanol molecules computed using the quantum-chemical GAMESS package with a set of independent vibrational coordinates in the approximations B3LYP/acc-pVQZ and B3LYP/6-311G**, respectively, have been transformed to a set of redundant vibrational coordinates. It has been shown that the use of the transformed...

A technique was suggested to transform ab initio molecular force fields calculated using a set of independent vibrational coordinates into a form corresponding to a complete set of regundand coordinates and reflecting the molecular symmetry. Conditions necessary for the appropriate transformations to be possible are formulated. The possibility of t...

Vibrational Raman and FT-IR absorption spectra of 4,4-methylene diphenyl diisocyanate (MDI) have been recorded. The ab initio and density functional theory calculations (B3LYP/cc-pVDZ) have been performed for the MDI geometric structure and force field. The fully optimized structure has been obtained using Quadratic Approximation gradient method an...

Low-temperature FTIR spectra of methanol in an argon matrix are analyzed on the basis of B3LYP/cc-pVTZ and B3LYP/acc-pVQZ calculations of the geometry and IR spectra of methanol monomer and dimer. The adequacy of the scaled force fields is checked by the comparison of the calculated and experimental spectra of methanol isotopomers. Assignment of th...

We present results of ab initio calculations of the structure and vibrational IR spectrum for 4,4-diphenylmethane-bis(methyl)carbamate (DPMC). Calculations were carried out in the HF/6-311G approximation with subsequent force-field scaling. The calculated characteristics of the vibrational spectrum of DPMC show satisfactory agreement with experimen...

We present calculated intensity distributions in torsional, rotational, and torsional-rotational Raman lines in spectra of hydrogen peroxide. Ab initio calculations of polarizability tensor components as functions of internal rotation angle were carried out in the HF/6-311G approximation. It is shown that the structure and transformational properti...

We present results of ab initio and DFT calculations of the structure, potential function of internal rotation of the methyl group, and vibrational frequencies and intensities in IR and Raman spectra of methylphenylcarbamate. The calculations were carried out in different basis sets in the HF, MP2, and DFT/B3LYP approximations with partial force fi...

We present results of ab initio and DFT calculations of the structure, potential functions of the methyl group internal rotation and the amino group inversion, and vibrational frequencies and intensities in IR and Raman spectra of methylcarbamate. The calculations were carried out using different basis sets in the HF, MP2, and DFT/B3LYP approximati...

We present the calculated intensity distributions in torsional-rotational IR absorption bands of hydrogen peroxide. The torsional components of the band intensities have been calculated based on the appropriate matrix element computations. The contribution of the rotational components has been calculated using the 3j-symbols technique. The calculat...

We present theoretical models and results of calculations of the energies of torsional states of dihydroxybenzenes: flexible molecules with two non-coaxial internal tops of low symmetry.

We present the calculated intensity distribution for bands and lines in torsional IR and Raman spectra of dihydroxybenzenes. The calculations were based on calculated matrix elements for the components of the dipole oment and the polarizability tensor.

We have obtained an analytical expression for the two-dimensional potential energy function for internal rotation in 1,2-dihydroxybenzenes, allowing us to use perturbation theory methods to calculate and interpret the torsional spectra of these compounds.

We show that electron-vibrational interaction (Renner effect) in the model of linear configuration of the hydrogen peroxide molecule leads to removal of degeneracy of the electronic state and is the determining factor for the existence of two dissimilar nonplanar equilibrium symmetrically equivalent configurations.

The incorrectness of solution of a torsional-rotational equation for asymmetric nonrigid molecules in the system of internal axes is shown; this incorrectness is caused by the broken interrelationship between the torsional quantum number and the parity of the rotational quantum number K.

A method for constructing the torsion potential function of hydrogen peroxide and disulfan molecules which takes into account the magnitudes of intramolecular interactions is suggested. The new representation of the potential is used to calculate the torsion spectra of the molecules indicated.

Based on the solution for the Mathieu equation, we obtained wave functions for the internal rotation of an ethane molecule that satisfy the symmetry properties of the group G36. We calculated the frequency of the principal torsional transition (273 cm−1). The types of symmetry of the energy levels and transition probabilities in IR and Raman spectr...

An x-ray diffraction structural analysis gave the geometrical parameters of 4,4'-dimethoxydibenzoyl peroxide and dibenzoyl peroxide. The Raman spectra were also taken for these two peroxides. The introduction of electron-donor substituents into dibenzoyl peroxide causes a decrease in the COOC dihedral angle, ?C=O frequency and strength, of the O-O...