INTRAMOLECULAR V-V TRANSFER BETWEEN THE COMPONENTS OF THE (3(1) 2(1)4(1)5(1)) AND (3(1)4(1)/2(1)4(2)5(1)) FERMI DYADS IN ACETYLENE IN C2H2-C2H2 COLLISIONS/

Infrared-ultraviolet double resonance experiments have been performed to determine rate coefficients for collisional intramolecular vibratio n-vibration transfer in pure acetylene within two Fermi dyads: (a) tha t formed from almost equal mixtures of the zero-order, normal-mode sta tes \3(1)> and \2(1)(4(1)5(1))(0)> and (b) that which is composed pred ominantly of the \3(1)4(1)(1)>, \2(1)4(2)(2)5(1)(-1)> and \2(1)4(2)(0) 5(1)(1)> states. Pulses of tunable IR excited molecules to the lower c omponent (II) of one of the Fermi dyads and the evolution of populatio n in the upper component (I) was observed by exciting laser-induced fl uorescence (LIF) from this level using tunable UV laser radiation(1). Analysis of the LIF signals vs. time yields the following rate coeffic ients (k(id)) for intradyad transfer at 295 K: for (3(1)/2(1)4(1)5(1)) (I <----> II), k(id) = (2.1 +/- 0.2) x 10(-10) cm(3) molecule(-1) s(-1 ); for (3(1)4(1)/2(1)4(2)5(1))(I <----> II), k(id) = (3.2 +/- 0.6) x 1 0(-11) cm(3) molecule(-1) s(-1). These results are discussed in terms of the matrix elements for such collision-induced transitions and diff erences in the mixing of the zero-order states in these two pairs of F ermi dyads. (C) 1998 Elsevier Science B.V. All rights reserved.