Calculations of Argon broadening and shift for HCO+ rotational lines at 77K

Different methods of calculations are compared to experiments at 77 K for t he broadening Gamma and shift s of some HCO+ rotational transitions by coll isions with Argon. Capture method and Anderson, Tsao, and Curnutte (ATC) me thod with straight line trajectories are both not able to reproduce the tre nd of Gamma with J. A discussion of the origin of such a discrepancy allows to obtain better insights into the different causes of collisional relaxat ion. Quite good agreement is obtained by both a hybrid method or ATC calcul ations using a more realistic translational dynamics. However, some discrep ancy still exists for high J values. (C) 1999 American Institute of Physics . [S0021-9606(99)00729-1].