G. Intramolecular Vibrational‐Rotational Redistribution, Anharmonic and Rovibronic Interactions. Vibrational Overtone Spectra of Jet‐Cooled CF3H by Infrared Laser Assisted Photofragment Spectroscopy

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Abstract
Using our recently developed technique of infrared laser assisted photofragment spectroscopy (IRLAPS), we have measured four vibrational overtone bands of jet‐cooled CF3H in the N = 4 and N = 5 CH stretch‐bend polyads. The cooling in the expansion eliminates much of the rotational congestion and reveals homogeneous structure which reflects the vibrational coupling of the stretch bend states with other modes of the molecule. This homogeneous structure indicates that the coupling of the stretch‐bend states to the rest of the molecule is 20–2000 times weaker than the stretch bend coupling itself and implies a hierarchy of time scales in the vibrational energy redistribution of the excited molecule. The overtone spectra of the jet‐cooled molecules also reveal a wide variation in the coupling strengths of the stretch‐bend states to the other modes, suggesting that the coupling depends upon the presence of specific low‐order resonances rather than on the total density of states.