15min:

ANGELA P. MILCE AND BRIAN J. ORR, School of Chemistry and Centre for Lasers and Applications, \newline Macquarie University, Sydney, NSW, Australia 2109.

Time-resolved fluorescence-detected infrared-ultraviolet optical double resonance (IR-UV DR) experiments have been used to obtain detailed measurements of spectroscopic and dynamical processes in the "_CC+ 3_CH" region of acetylene (C₂H₂) at 11 600 cm^-1. The rotational energy transfer (RET) and vibrational energy transfer (V-V) kinetic data collected have already been well fit to a detailed rate-equation model that incorporates empirical exponential-gap fitting laws. \footnoteA.~P.~Milce, H.~-D.~Barth and B.~J.~Orr, J.~Chem.~Phys. \underline\textbf100, 2398 (1994); A.~P.~Milce and B.~J.~Orr, J.~Chem.~Phys. \underline\textbf104, 6423 (1996); ibid. \underline\textbf106, (1997) in print.

In order to explain some of the unusual effects observed in this region we now use the cluster/polyad model that has already successfully interpreted the vibrational energy pattern in C₂H₂ up to 12 000 cm^-1. \footnote M.~A.~Temsamani and M.~Herman, J.~Chem.~Phys. \underline\textbf102, 6371 (1995); ibid. \underline\textbf105, 1355 (1996); M.~A.~Temsamani, M.~Herman, S.~A.~B.~Solina, J.~P.~O'Brien and R.~W.~Field, J.~Chem.~Phys. \underline\textbf105, 11357 (1996). Our work emphasises rotational perturbations, after including the rotational l -type resonance interaction. This enables us to identify the intramolecular couplings responsible for enhancement of rotationally-resolved V-V energy transfer between coupled rovibrational levels of the "_CC+ 3_CH" manifold. The model also provides qualitative evidence that Coriolis-type perturbations are responsible for other unusual symmetry-breaking phenomena in this region.