Ground and Low-Lying Excited Electronic States of Difluorodiazirine

Abstract

Ground and low-lying excited electronic states of difluorodiazirine (F2CN2) were investigated using the recently revised, multireference, second-order generalized Van Vleck perturbation theory (GVVPT2). Initial studies on the ground state were carried out with the single-reference Moller−Plesset second order perturbation theory (MP2), quadratic configuration interaction with single and double excitation (QCISD), and coupled cluster with single, double, perturbative triple excitations (CCSD(T)) methods using several correlation-consistent atomic basis sets. MP2 and QCISD did not give semiquantitatively correct descriptions of the ground state of the molecule. For the ground state, GVVPT2 results are in close agreement with CCSD(T) but lie slightly closer to the experimental results. A balanced treatment of nondynamic and dynamic correlation effects has been shown to be of crucial importance for correct description of the system. Equilibrium geometries, excitation energies, and thermodynamic stabilities of ...