Isotopically selective collisional vibrational energy transfer in CF3H

The authors investigate here the mechanism of collisionally enhanced isotopic selectivity observed in infrared multiple photon dissociation (IRMPD) of vibrationally preexcited CF3H by Boyarkin et al. [J. Chem. Phys. 118, 93 (2003)]. For both the carbon-12 and carbon-13 isotopic species they measure the dependence of the IRMPD yield on the time delay between the preexcitation and the dissociation pulses at different dissociation frequencies as well as its dependence on the initial isotopic composition of the sample. The results reveal that the collisional increase in isotopic selectivity originates not only from that of IRMPD itself but also from the isotopic selectivity of vibrational energy transfer, with the latter making the major contribution under their experimental conditions. They suggest that the observed isotopic selectivity in collisional energy transfer arises from the difference in overlap between the absorption spectra of the nu5 mode in the 12CF3H acceptor molecule with emission spectra of the same mode in the two isotopically different donors. Understanding the origin of this collisional effect has important implications for optimization of laser isotope separation processes.