Vibration→Vibration Energy Transfer in Hydrogen Chloride Mixtures

Abstract

Laser-excited vibrational fluorescence experiments on HCl mixtures have given cross sections for vibration→vibration energy transfer from HCl to other molecules: σHCl→HBr = (2.1 ± 0.2) × 10−17 cm2, σHCl→N2 = (4.2 ± 0.4) × 10−19cm2, σHCl→HI = (3.5 ± 0.5) × 10−18cm2, σHCl→CO = (1.3 ± 0.15) × 10−18cm2, σHCl→DCl = (1.66 ± 0.1) × 10−18cm2, σHCl→CH4 = (3.7 ± 0.3) × 10−17cm2, and σD2→HCl (transfer from D2to HCl) = (2.1 ± 0.2) × 10−17cm2. The cross sections are considerably larger than for other diatomic–diatomic systems and decrease comparatively slowly with increasing energy difference between the vibrational levels. This behavior may result from strong “chemical” intermolecular forces, from energy transfer to rotation, and from the large amplitude of hydrogen atom stretching vibrations. The lack of a smooth correlation between cross section and energy difference illustrates the importance of the nature of the collision partners.