ROTATIONAL ENERGY-TRANSFER AND ROTATIONALLY SPECIFIC VIBRATION-VIBRATION INTRADYAD TRANSFER IN COLLISIONS OF C2H2(X)OVER-TILDE(1)SIGMA(+)(G)(3(1) 2(1)4(1)5(1),J=10) WITH C2H2, AR, HE AND H-2/

Infrared-ultraviolet double resonance (IRUVDR) experiments have been p erformed on samples of pure C2H2 and on C2H2 diluted in Ar, He and H-2 . Pulses of tunable IR radiation from an optical parametric oscillator (OPO) excited molecules of C2H2 to the J = 10 rotational level of the lower component state (II) of the (3(1)/2(1)4(1)5(1))(II) Fermi dyad in the (X) over tilde (1)Sigma(g)(+) electronic ground state of C2H2 a nd tunable UV radiation was used to record laser-induced spectra at sh ort delays. In this way, state-to-state rate coefficients have been de termined for two kinds of processes: (a) rotational energy transfer (R ET) induced by collisions with C2H2, Ar, He and H-2 from the initial l evel J(i) = 10 to other levels (J(f) = 2-8, 12-20) within the same com ponent (II) of the (3(1)/2(1)4(1)5(1)) Fermi dyad, and (b) intradyad t ransfer in C2H2-C2H2 collisions to specific levels (J(f) = 2-14, 18) i n the other component (I) of this Fermi dyad. Transfer from II to I is found to account for ca. 16% of the total relaxation from (II, J(i) = 10). The distribution of state-to-state rate coefficients for RET bec omes broader as the mass of the collision partner increases, in accord with the predictions of a simple classical model. Absolute values of the state-to-state rate coefficients are determined by scaling the res ults to the previously determined rate coefficients for rotational rel axation by the same collision partner. It is suggested that intradyad transfer is relatively facile because of the difference in the two dia gonal terms in the vibrational matrix element for the transition, with the [2(1)4(1)5(1)\V\2(1)4(1)5(1)] component being larger than the [3( 1)\V\3(1)] component.