Rotational Transition of CO2 Molecule by Collisions

The quantum-mechanical method of distorted waves for calculating the rotational relaxation rates in H2 as developed by Brout is used here to calculate the relaxation time for the ΔJ=±2 rotational transitions of linear polyatomic CO2 by taking into account the higher partial wave contributions. The intermolecular potential used consists of a spherical part and a nonspherical part with a constant parameter to characterize the deviation of the potential from spherical symmetry. The results obtained indicate that the collision number Z (and hence the relaxation time τ) is a monotonically decreasing function of the temperature T for a given J and is a monotonically increasing function of J for a given T. Except for small values of J, Z and τ for a given T are both approximately proportional to exp(aJ), where a is a constant. Detailed numerical results are also obtained and compared with known experimental results. It is shown that the method used here is not valid when the temperature is too high or whenever Z becomes too close to 1.