Carbon suboxide as a quasilinear molecule with a large amplitude bending mode: Determination of the molecular constants and the ν7 potential function

Abstract

The model of a quasilinear molecule with a large amplitude bending mode is used to treat C 3O 2. The Hamiltonian operator, including the rotation-vibration interaction, is derived allowing only a single vibrational degree of freedom, namely, the ν 7 mode corresponding to the bending at the central carbon atom. The CCO angle is constrained to be 180°. With this model the rotational energy levels and, thus, the molecular constants can be computed for any ν 7 level once the ν 7 potential is specified. The l-doubling is included only for π 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 ν7 0 states. The resulting ν 7 potential has a 30.56 cm −1 barrier at α = 0 with a minimum at α = 11.04°, where 2α is the angular deviation from linearity. The model gives a good fit to the 2 ν 7 Raman data and to the rotational and centrifugal distortion constants in all of the nν7 l states which have been analyzed. A similar analysis is applied with equal success to the states with ν 4, the asymmetric CC stretch mode at 1587 cm −1, simultaneously excited with a ν 7 mode. The potential in this case has a 56.58 cm −1 barrier at α = 0 with a minimum at α = 13.02°.