Collision induced relaxation of an electronically excited molecule: Evidence for low energy resonance enhanced vibrational deactivation

The paper reports a study of collision induced vibrational relaxation of electronically excited iodine. A novel technique is used to probe the energy dependence of the collision cross section, namely, variation in the position of illumination along the axis of a supersonic free jet. Experimental results are reported which indicate that the relaxation induced by collisions with extremely small relative kinetic energy is very efficient. The evidence available is consistent with a model in which the vibrational deactivation is enhanced by orbiting resonances or rotational resonances of the colliding pair