A scattering resonance description of very low energy collision induced vibrational relaxation.

We report a study of very low energy collision induced vibrational relaxation using an approximate resonant state formalism which relates the inelastic cross section to the properties of metastable states. A study of models loosely based on the He+I2 (B 3Π0+u) system reveals that the combined effect of a low collision energy resonance and high initial diatomic vibrational excitation can lead to a large enhancement of the vibrational relaxation cross section. However, even in the absence of resonances the cross section, for very low energies, increases with decreasing energy. It is found that this effect increasingly enhances the contribution of a resonance to the cross section the closer the resonance is to zero collision energy. Because the density of resonances near zero collision energy is small the collision dynamics near zero collision energy is very sensitive to the nature of the potential energy surface. [ABSTRACT FROM AUTHOR]