Theoretical Investigations of Translation—Rotation Energy Transfer. II. Semiclassical Treatment of (p-H2, He) and (o-D2, He) Systems

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Abstract
A semiclassical analysis of translation—rotation energy transfer in (p—H2, He) and (o‐D2, He) systems is reported. The Krauss—Mies potential surface has been employed to calculate 0→2 rotational excitation cross sections as a function of relative velocity and attractive well depth. For a well depth of 1.675×10−3 eV, the (p‐H2, He) cross sections range from 0.54 to 1.144 Å2 at relative velocities of 4.5×105 and 8.0×105 cm/sec, respectively. The (o‐D2, He) cross sections vary from 1.382 to 1.461 Å2 for relative velocities of 4.5×105 and 6.0×105 cm/sec, respectively. A maximum in the excitation cross section is observed at a relative energy of about 0.427 eV for the (p‐H2, He) system and at 0.27 eV for the (o‐D2, He) system. In both systems the calculated cross sections increase with increasing attractive well depth. Consideration of intermultiplet transitions in the (p‐H2, He) system indicates that inclusion of such transitions is unimportant in systems of this type. Comparison with previous classical calculations employing the same potential surface indicates that the classically calculated cross sections are probably high by at least a factor of 2. Calculated cross‐section ratios, however, are in good agreement with the present results. Semiquantitative agreement between classical and semiclassical results is obtained with regard to the dependence of the cross sections on attractive well depth and the variation of the excitation probability with the He attack angle. It is concluded, in general, that the extent of agreement between the models is sufficient to justify the use of classical models to treat the purely quantum phonomenon of transitions between specific energy states.