Carbon suboxide as a quasilinear molecule with a large amplitude bending mode : Determination of the molecular constants and the [nu]7 potential function

Abstract

The model of a quasilinear molecule with a large amplitude bending mode is used to treat C3O2. The Hamiltonian operator, including the rotation-vibration interaction, is derived allowing only a single vibrational degree of freedom, namely, the [nu]7 mode corresponding to the bending at the central carbon atom. The C=C=O angle is constrained to be 180[deg]. With this model the rotational energy levels and, thus, the molecular constants can be computed for any [nu]7 level once the [nu]7 potential is specified. The l-doubling is included only for [pi] states. The model contains three adjustable parameters: the rotational constant in the linear configuration and two terms in the potential function, and these are determined by fitting three experimental quantities: the rotational constants in and the separation between the ground and 2[nu]70 states. The resulting [nu]7 potential has a 30.56 cm-1 barrier at [alpha] = 0 with a minimum at [alpha] = 11.04[deg], where 2[alpha] is the angular deviation from linearity. The model gives a good fit to the 2[nu]7 Raman data and to the rotational and centrifugal distortion constants in all of the n[nu]7l states which have been analyzed. A similar analysis is applied with equal success to the states with [nu]4, the asymmetric C=C stretch mode at 1587 cm-1, simultaneously excited with a [nu]7 mode. The potential in this case has a 56.58 cm-1 barrier at [alpha] = 0 with a minimum at [alpha] = 13.02[deg].