ENHANCED INSTABILITY OF EXTREME MOTION STATES IN PROPYNE - LIFETIMES OF OVERTONE VERSUS ISOENERGETIC COMBINATION STATES

In contrast to the theoretical and experimental evidence for small pol yatomic molecules, we demonstrate that in the low overtone region of p ropyne (nu(CH) = 2-4) pure overtone states are more perturbed by intra molecular vibrational energy redistribution (IVR) than some nearly iso energetic combination states. We argue that for larger molecules, this is the expected behavior when the combination states have their energ y delocalized over modes that interact only weakly by direct low order anharmonic resonances.