The unimolecular reaction of isolated CF3CN: Energy disposal into CN product degrees of freedom

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Abstract
Measurements of nascent CN rovibronic state distributions following the unimolecular reaction CF3CN→CF3+CN are reported. Excitation under collision‐free conditions is provided by IR multiple photon excitation using the focused output from a CO2‐TEA laser, and therefore reaction occurs from a range of energies E≠, centered at some value which is determined by the laser intensity. Nascent reaction products are detected by laser induced fluorescence (LIF), and, by exciting the Δv = 0,−1, and −2 sequences of the B 2Σ+←X 2Σ+ system, rotational distributions can be determined for v″ = 0,1, and 2 with no interference. Rotational excitation in v″ = 0–2 is the same for each v″ and can be described by a Boltzmann distribution with TR = 1200±100 K. Product translational energies are estimated by monitoring LIF intensities as a function of the delay between the onsets of the CO2 and dye laser pulses. Translational energies do not change over the range v″ = 0–4, and can be ascribed a temperature of 850±150 K. CN vibrational excitation is determined by simulating the LIF spectra, and can be described by TV = 2400±150 K based on v″ = 0–3, with v″ = 4 barely detectable. These results can be explained qualitatively using a statistically based model in which the CN vibration acts as a thermometer of parent excitation, and where parent nuclear motions, including vibrations as well as motions not influenced by potential energy, are in equilibrium at the transition state. The constancy of rotational and translational excitations with respect to v″ are seen to derive from the range of E≠ from which dissociation occurs.