ULTRAFAST COLLISIONAL REDISTRIBUTION OF VIBRATIONAL-ENERGY IN HIGHLY EXCITED POLYATOMIC-MOLECULES - THE ROLE OF INTRAMOLECULAR INTERACTIONS

Time-resolved Raman probing technique is used to investigate the colli sional relaxation of high-lying C-H vibrations in CHF3 and CHF2Cl mole cules. The relaxation rates both in collisions with parent molecules a nd 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 t ransfer from excited ''bright'' states to nearby ''dark'' ones. Possib le mechanisms of the above transfer are discussed.