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 found.Different methods of the molecular parameters calculations were suggested and analyzed. The torsional, spin and total wave functions were classified by irreducible representations of the C2V(M) molecular symmetry group. The 2D dipole moment surface was calculated too. The energies of the stationary torsional states were found using DVR and Fourier methods. With this and acceptable combinations of spatial and spin wave functions, the IR torsional spectrum was calculated at different temperatures. The tunneling frequencies in the ground and some excited torsional states were estimated too.
Torsional
vibrations of a 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 potential energy
and kinematic coefficient surface calculations. These calculations
were made at the MP2/cc-pVTZ and MP2/cc-pVQZ levels of theory, and
then the results were extrapolated to the complete basis set limit.
The 2D surface of the zero-point vibrational energy of a sulfoxylic
acid molecule was calculated at the MP2/cc-pVTZ level of theory in
anharmonic approximation and taken into account. The energies of the
torsional states were found by numerical solution of the vibrational
Schrödinger equation of the restricted dimensionality using
the Fourier method. 2D surfaces of the dipole moment components were
calculated too. Using all these data, the torsional IR spectra of
the trans- and cis-conformers of the HOSOH, DOSOD, and DOSOH molecules
were also modeled at different temperatures.
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. Additionally, calculations of the 2D surface of zero point vibrational energy of the molecule in the harmonic and anharmonic approximations were performed at MP2/Aug-cc-pVTZ level of theory. The zero point vibrational energy calculated in two approximations is summed up with the potential energy of the methyl hydroperoxide molecule, calculated at two levels of theory, and the resulting four outcomes of the refined potential energy are used to calculate the energies of stationary torsional states and tunneling frequencies. The results obtained are compared with the experimental and theoretical data presented in the literature to evaluate the efficiency of taking into account the zero point vibrational energy when examining the internal rotation in molecules.
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