INFRARED ULTRAVIOLET DOUBLE-RESONANCE MEASUREMENTS ON THE RELAXATION OF ROTATIONAL ENERGY IN THE (3(1), 2(1)4(1)5(1)) FERMI RESONANCE STATES OF C2H2

Infrared-ultraviolet double resonance experiments have been performed to measure total rotational relaxation rates from a single, selected level in C2H2 induced by a variety of collision partners (M). Pulses of tunable infrared radiation from an optical parametric oscillator have been used to excite C2H2 molecules into a rotational level within one or other of the vibrational states arising from Fermi resonance between the zeroth-order 3(1) and 2(1)4(1)5(1) states. Loss of population from this level was observed by making time-resolved laser-induced fluorescence measurements on the appropriate lines in the A 1A(u) - X 1-SIGMA(g)+ electronic bands of C2H2. Rate constants are presented for relaxation from the j = 12 level of the lower of the Fermi dyads with M = C2H2, He, Ne, Ar, Kr, Xe, H-2, N2, O2, CO, NO, HCl, HBr and HCN. A smaller number of results are presented for relaxation from other levels and the data are discussed in the light of energy transfer rates and collision-broadening parameters measured previously for rotational levels in other vibrational states.