An examination of the corrected centrifugal sudden approximation for the calculation of line broadening and shifting coefficients for HF in He

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Abstract
By utilizing the lineshape theory of Shafer and Gordon [J. Chem. Phys. 58, 5422 (1973)], pure rotational pressure broadening and shifting coefficients for the infrared spectral lines of HF in He have been calculated using the close-coupled (CC) method, the centrifugal sudden (CS) approximation, and the corrected centrifugal sudden (CCS) approximation of McLenithan and Secrest [J. Chem. Phys. 80, 2480 (1987)]. Comparison of the results obtained from these three methods were made at the total angular momentum dependent, kinetic energy dependent, and temperature dependent levels. In the latter comparisons, a semiclassical method was also included. The CS results agree very well with the CC calculations for the pressure broadening coefficients, but deviate slightly for the pressure shifting coefficients. The CCS results were essentially identical to those obtained from the CS approximation calculations. The semiclassical method was accurate to within about 15% of the CC values for the pressure broadening coefficients. The pressure shifting coefficients have been found to be very sensitive to the number of closed channels included in the calculations. As well, while collisionally inelastic contributions to the effective cross sections were not found to be negligible, their effect on the final calculated pressure broadening and shifting coefficients was found to be insignificant for this particular system at room temperature.