Decomposition of highly vibrationally excited CDCl3

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Abstract
Decomposition of highly vibrationally excited CDCl3 was studied in the time domain by measuring laser‐induced fluorescence from one of the decomposition products CCl2 or by observing luminescence from CCl2 radical fragments produced in the Ã(1B1) state following IR excitation. It is shown that highly vibrationally excited CDCl3 can be made via two different routes: i/mple optical absorption of an incident 13CO2 laser pulse or through collision‐moderated energy pooling coupled with photon absorption. Higher fluence measurements are consistent with the former and support previous claims that the infrared multiphoton decomposition probability for CDCl3 is pressure independent. At a lower fluence the vibrational up‐pumping mechanism apparently relies heavily upon collisions, which supports other claims that the decomposition probability is pressure dependent. The results of the present work reconcile these previous disparate claims. Furthermore, there is an indication that the vibrational energy transferred during a collision could be much larger than collision‐induced dipole selection rules would allow. In some of the experiments, electronically excited CCl2 fragments are created but only through post‐laser‐pulse collisions that appear to involve exchanges of very large amounts of vibrational energy. By contrast, no electronically excited CCl2 is produced following excitation with the CO2 laser alone. The experiments also corroborate an earlier prediction that the extent of reaction is governed by adiabatic expansion of the centrally heated zone, even at pressures as low as 0.66 kPa, rather than by diffusion, as is commonly believed.