RELAXATION WITHIN AND FROM THE (3(1) 2(1)4(1)5(1)) AND (3(1)4(1)/2(1)4(1)5(1)) FERMI DYADS IN ACETYLENE - VIBRATIONAL-ENERGY TRANSFER IN COLLISIONS WITH C2H2, N-2 AND H-2/

Infrared-ultraviolet double resonance (IRUVDR) experiments have been p erformed on samples of pure C2H2 and on C2H2 diluted in N-2 and H-2. P ulses of tunable IR radiation from an optical parametric oscillator (O PO) excited molecules of C2H2 to one component state of one of two Fer mi dyads in the (X) over tilde (1)Sigma(g)(+) electronic ground state, i.e. (3(1)/2(1)4(1)5(1))(II) or (3(1)4(1)/2(1)4(2)5(1))(II), and tuna ble UV laser radiation was used to observe the evolution of population either in that state or in the other component state of the same Ferm i dyad. In this paper,double dagger rate coefficients are reported for two kinds of processes: (a) vibration-to-vibration (V-V) transfer bet ween the two component states of the same Fermi dyad induced by collis ions with C2H2, N-2 and H-2, and (b) vibrational relaxation from the c oupled pair of Fermi dyad states in collisions with the same gases. In addition, populations have been observed in the (4(2)5(1)), (4(1)5(1) ) and (4(2)) states of C2H2 during relaxation from the (3(1)4(1)/2(1)4 (2)5(1)) dyad and rate coefficients for self-relaxation from the first two of these states have been derived. The results for both V-V intra dyad transfer and for vibrational relaxation are discussed in terms of the vibrational matrix elements for such collision-induced transition s and differences in the mixing of the zero order states in the Fermi dyads.