Rovibrational relaxation in collisions between molecules: I. Transitions induced by ground state para-

We present the results of quantal calculations of cross sections and rate coefficients for rovibrational transitions in ortho- and para- , induced by collisions with ground state para- . Rovibrational levels up to were included in the calculations, and rate coefficients are available for temperatures . Comparison is made with previous calculations and with measurements of the rate coefficient for vibrational relaxation . Agreement is found to be good at both high and low temperatures, but the measurements exceed the calculations at intermediate temperatures. Large discrepancies are found with previous calculations, which employed a semiclassical method.