The Production of Rotational and Vibrational Transitions in Encounters between Molecules

Abstract

Publisher Summary This chapter focuses on the production of rotational and vibrational transitions in molecular encounters. Vibrational transitions are infrequent in most diatomic gases at or below room temperature, so that the distorted wave method provides reliable results. However, they may be affected considerably by rotational transitions as these increase or decrease the change in the translational energy. Furthermore, the relative orientation of the colliding molecules influences the vibrational transition probabilities. After a series of rotational transitions, the molecules may tend to have a particular relative orientation at the instant of the vibrational transition. Rotational transitions must be studied in detail before vibrational transitions can be treated. If the duration of the encounter is longer than the period of molecular rotation and vibration, and the distortion is nearly adiabatic, there is another appropriate set of basic functions sometimes used in the treatment of atomic collisions—the perturbed stationary state (PSS) wave functions. Unless the energy of relative motion is high, PSS functions provide a good basis for treating rotational transitions in collisions between strongly polar molecules, vibrational transitions of a molecule with a small force constant, and both rotational and vibrational transitions in collisions between chemically reactive molecule.