Vibrational Energy Flow in the Ground Electronic States of Polyatomic Molecules

Rovibrational Energy Transfer in the 4νCHManifold of Acetylene Viewed by IR−UV Double Resonance Spectroscopy. 2. Perturbed States withJ= 17 and 18

“…It has therefore not been feasible to measure collision-induced Δ J = 0 energy transfer between them and to test how that is affected by the intramolecular perturbations. Following conventional expectations, − , it might be presumed that collision-induced energy transfer between two such strongly coupled rovibrational eigenstates will “invariably” 6 be highly efficient. However, that is by no means certain, given our contrary experience 7-9 in the classic case of Fermi resonance 87 between the (1 0 0 0, 0 2 0 0) I and (1 0 0 0, 0 2 0 0) II vibrational manifolds of CO 2 , where destructive interference between relatively uncongested quantum-mechanical channels are predicted 7-9 to yield an unexpectedly low energy-transfer efficiency, consistent with experiment .…”

“…Collision-induced state-to-state energy transfer in congested rovibrational energy manifolds of polyatomic molecules in the gas phase has long been of interest, both intrinsically − and in other contexts such as unimolecular reaction dynamics − and intramolecular vibrational redistribution. ,− It remains a challenge to characterize collision-induced energy transfer involving highly excited rovibrational states of small polyatomic molecules with just a few atoms (e.g., 3−6). Such investigations provide useful comparisons (and contrasts) with corresponding studies of the more highly congested rovibrational manifolds in larger polyatomic molecules. ,− This interface between the dynamics of large and small molecules is well-exemplified by the series of experiments by Flynn and co-workers on intermolecular rovibrational energy transfer between large donor molecules such as highly vibrationally excited pyrazine and a “bath” of small acceptor molecules such as CO 2 21 or CO …”

“…Of special concern in this paper is the extent to which the rovibrational manifold of interest is affected by intramolecular perturbations and how this may affect collision-induced state-to-state rovibrational energy transfer. Previous investigations of supposedly uncomplicated small polyatomic molecules, such as CO 2 , − , CH 3 F, ,,, and formaldehyde (H 2 CO, HDCO, D 2 CO), − ,− have provided useful insights in this regard. Expectations 3-6,24 that “a greatly enhanced energy transfer is invariably found” 6 in the presence of strong intramolecular perturbations are not in fact always realized. − It has been demonstrated 7-9 that quantum-mechanical interference mechanisms can sometimes cause the probability of collision-induced energy transfer to be inhibited rather than enhanced within moderately congested rovibrational manifolds where intramolecular perturbations prevail.…”