A PREDICTION OF THE VIBRATION-ROTATION ABSORPTION SPECTRA OF THE D216O MOLECULE ν2 BAND BY SOLVING THE OPERATOR PERTURBATION THEORY DIRECT PROBLEM AND A REFINEMENT OF THE EFFECTIVE ROTATIONAL HAMILTONIANS

Abstract

By means of solving the direct vibration-rotation problem with the Watson Hamiltonian by the operator Van Vleck perturbation theory and using the quantum chemical (CCSD(T)/aug-cc-pVQZ) geometrical molecular structure, sextic force field and cubic dipole moment surface of the D216O molecule, the absorption spectra and spectroscopic constants of effective rotational Hamiltonians in A-reduction were predicted for the ground state and ν2 band. The theoretic sixth order perturbative approach in vibrational variables (fourth for the dipole moment operator) and third order in rotational variables is based on the systematic procedure of calculating rotational commutators by means of normal ordering of cylindrical angular momentum operators. The obtained reduced spectroscopic constants were refined and augmented using fitting to experimental energy levels. It is shown that new effective Hamiltonians significantly better reproduce experimental data for J ≤ 30, while calculated intensities reproduce experimental counterparts with the high accuracy.