Ultrafast Collisional Redistribution of Vibrational Energy in Highly Excited Polyatomic Molecules. The Role of Intramolecular Interactions

摘要

Time-resolved Raman probing technique is used to investigate the collisional relaxation of high-lying C-H vibrations in CHF_3 and CHF_2Cl molecules. The relaxation rates both in collisions with parent molecules and a number of buffer gases were measured. The rate values were found to be abnormally fast. The relaxation is faster than single collision in parent gas and requires a few (3-8) collisions for nonpolar gases. For polar gases the relaxation is still faster. The conclusion is made that observed ultrafast relaxation of C-H modes is caused by energy transfer from excited "bright" states to nearby "dark" ones. Possible mechanisms of the above transfer are discussed.