Mechanism and rates of rotational relaxation of CO2(001) in He and Ar

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Abstract
Cross sections and rate constants for rotational relaxation of C02(001) in He and Ar are calculated using realistic (electron gas plus van der Waals) potential energy surfaces and 22 000 classical trajectories. Some propensity for small Δj transitions over large Δj transitions is noted, but there is certainly n o Δj=±2 selection rule, and transitions with Δj as large as 30 are important in the relaxation kinetics. Calculated rates are compared with experiment and found to be within a factor of 2 for the total rate of relaxation into a depleted level. Relaxation of levels other than the depleted level is also modeled, and it is found that the present method, in contrast to earlier models, gives excellent agreement with experiment. It is suggested that the transitions used in multiline energy extraction from CO2laser amplifiers be spread out rather than adjacent.