Rotational Transition of Hydrogen Molecule by Collision

The previous calculation of rotational transition probability for para-hydrogen gas is improved by adding an attractive term to the intermolecular potential. Using the result of recent calculations by Evett and Margenau of intermolecular force, good agreement is obtained between the calculated and experimental values of transition probability. The transition probability is also calculated for H 2 -H collisions, because of its importance for the cooling of interstellar matter. According to our present knowledge of the intermolecular forces the H 2 -H potential shows much more appreciable anisotropy than does the H 2 -H 2 potential, so that H 2 -H collisions are much more effective than H 2 -H 2 collisions for the rotational transition, nearly 10 times for 100-1000°K.