Hydrogen bonded pyridine N-oxide/trichloroacetic acid complex in polar media: 2D potential energy surface and O–H⋯O vibration analysis using exact vibrational Hamiltonian

A convenient set of vibrational coordinates for 2D calculation of the tunneling splittings of the ground state and some excited vibrational states for the inversion motion in H3O+, H3O-, and H3O

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 oxygen atom from the plane of a regular triangle formed by three hydrogen atoms and 2) a symmetry coordinate composed of three distances between chemically non-bonded hydrogen atoms. The kinetic energy operator in this case takes the simplest form. The 2D potential energy surface (PES) in the given coordinates was calculated for H₃O⁺ at the CCSD(T)/aug-cc-pVTZ and CCSD(T)-F12/cc-pVTZ-F12 levels of theory. The same 2D PES for the H₃O^- anion and H₃O radical were calculated at the CCSD(T)/aug-cc-pVQZ, CCSD(T)/d-aug-cc-pVQZ and UCCSD(T)/aug-cc-pVQZ, UCCSD(T)/d-aug-cc-pVQZ levels of theory, respectively. The tunneling splittings were calculated for the cations H₃¹⁶O⁺, D₃¹⁶O⁺, T₃¹⁶O⁺, H₃¹⁸O⁺, D₃¹⁸O⁺, T₃¹⁸O⁺. The tunneling splittings for the H₃O^-, D₃O^-, T₃O^- anions and H₃O, D₃O, T₃O radicals were calculated for the first time. The results of calculations demonstrate good agreement with experimental values of the tunneling splittings in the ground state and in some excited vibrational states of the H₃¹⁶O⁺ and D₃¹⁶O⁺ cations.

The role of sulfur interactions in crystal architecture: experimental and quantum theoretical studies on hydrogen, halogen, and chalcogen bonds in trithiocyanuric acid–pyridine N-oxide co-crystals

Hydrogen, halogen, chalcogen bonds and π interactions of the trithiocyanuric acid ring are responsible for crystal structure architecture and have been classified according to the QTAIM approach as closed-shell interactions.

Torsional States and Tunneling Probability in HOSOH, DOSOD, and DOSOH Molecules Analyzed at the CBS Limit

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.

Quantum aspects of torsional vibrations in the HO3H, DO3H and DO3D molecules

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 HO_nH (n ≥ 2). Due to this, it is the subject of close attention of researchers. In this paper, we performed a group theory analysis of the torsional and spin states of the HOOOH, DOOOH, and DOOOD molecules. The relationships have been established between the symmetry species of the C_2V(M) molecular symmetry group to which the HOOOH and DOOOD molecules belong, and the symmetry species of the C₂ and C_S point groups to which the equilibrium configurations of trans- and cis-conformers of the above molecules belong, respectively. 2D PES and 2D surfaces of kinematic coefficients related to torsional vibrations of hydroxyl groups were calculated at the complete basis set (CBS) limit by extrapolating the results of calculations at the MP2/cc-pVTZ and MP2/cc-pVQZ levels of theory. For all the three molecules, the energies of the stationary torsional states were computed using the Fourier method for a numerical solution of the 2D vibrational Schrödinger equation. Symmetry species of torsional states and the values of quantum numbers defining the types of torsional vibrations were found by analyzing the torsional wave functions. The selection rules for transitions between torsional states in the dipole approximation were also formulated.

Theoretical study of the C-H/O-H stretching vibrations in malonaldehyde

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 using the Cartesian coordinates of the hydroxyl hydrogen atom and the stretching coordinates of С-Н, C-D, O-H, and O-D bonds. It was shown that in each of the two equivalent forms of the molecule, besides the global minimum, an additional local minimum at the PES is formed with the energy more than 3,000 cm(-1) higher than the energy in the global minimum. Calculations carried out by constructing the 2D and 3D PESs indicate a high anharmonicity level and multiple manifestations of the stretching О-Н vibrations, despite the fact that the model used does not take into account the splitting of the ground-state and excited vibrational energy levels. In particular, the vibration with the frequency 3,258 cm(-1) may be associated with proton transfer to the region of a local minimum of energy. Comparing the results obtained with the experimental data presented in the literature allowed us to propose a new variant of bands assignments in IR and Raman spectra of the molecule in the spectral region 2,500-3,500 cm(-1).