Collisional rates for asymmetrical top molecules

Collisional rate coefficients for rotational transitions in C3H2 and SiC2 d ue to collisions with H-2 molecules are calculated. The C3H2 has two distin ct species, ortho and para, whereas the SiC2 has only ortho specie due to s pin statistics for the identical carbon nuclei. For ortho- and para-C2H2 we accounted for 47 and 48 energy levels, respectively. The calculations are done for the kinetic temperatures 30! 60, 90, and 120 K. For ortho-SiC2, we accounted for 40 energy levels and the calculations are done for the kinet ic temperatures 25, 50, 75, 100, and 125 K. The results are reported here f or the transitions in the upward direction. The values for the downward dir ection can easily be calculated with the help of the detailed equilibrium e quation.