Torsional IR spectra of three conformers of the resorcinol molecule

Abstract

Conformational states, barriers to internal rotation, 2D potential energy surfaces, kinetic coefficients and dipole moment components of the resorcinol molecule are calculated at the MP2/CBS(T,Q), MP2/Aug-cc-pVTZ, MP2/dAug-cc-pVTZ and B3LYP/Aug-cc-pVTZ levels of theory. After symmetrization of the calculated data, they were approximated by the symmetry-adapted sets of basis functions. Using the calculated data sets, the energies and wave functions of stationary torsional states were determined for the first time using a numerical solution of the vibrational Schrödinger equation of limited dimensionality. This made it possible to establish the values of the tunneling splitting of the ground vibrational and a number of excited torsional states of the energetically most preferred conformer of the molecule, belonging to the point symmetry group CS. The 100 lowest torsional states of the resorcinol molecule are classified according to the symmetry species of the molecular symmetry group C2V(M), which unites all three conformers of the molecule. The calculations of the matrix elements of the dipole moment operator and the partition functions made it possible to simulate the torsional IR spectra of three conformers of the molecule at different temperatures. The calculated values of the frequency of the most intense torsional vibration in the most stable conformer of the molecule (316 and 320 cm-1), obtained at the MP2/dAug-cc-pVTZ and MP2/CBS(T,Q) levels of theory are in good agreement with the experimental value of the frequency of this vibrations (318 cm-1), obtained in [W.G. Fateley, J.Phys.Chem., 79 (1975) 199 – 204.].