Computational study of the rovibrational spectra of CO2–C2H2 and CO2–C2D2

Abstract

An intermolecular potential energy surface and rovibrational transition frequencies are computed for CO2–C2H2. An interpolating moving least squares method is used to fit ab initio points at the explicitly correlated coupled-cluster level. The rovibrational Schrödinger equation is solved with a symmetry-adapted Lanczos algorithm. The computed disrotatory and torsion vibrational levels of both CO2–C2H2 and CO2–C2D2 differ from those obtained by experimentalists by less than 0.5cm−1. CO2–C2H2 has two equivalent minima with the monomers perpendicular to the inter-monomer axis. In contrast to many other Van der Waals dimers there is no disrotatory path that connects the minima. The tunnelling path follows the torsional coordinate over a high barrier and the splitting is therefore tiny. Using vibrational parent analysis we are able to fit and thus obtain rotational constants and centrifugal distortion constants. Calculated rotational constants differ from their experimental counterparts by less than 0.001cm−1.