Infrared multiphoton excitation dynamics of CF3I. I. Populations and dissociation rates of highly excited rovibrational states

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Abstract
Transient detection of I(2P3/2) by resonantly enhanced multiphoton ionization (REMPI) was used to monitor in-pulse and after-pulse dissociation of CF3I excited by infrared (IR) multiphoton absorption. After-pulse reaction is characterized by time-dependent dissociation rate coefficients. The apparent reaction rates increase with increasing laser intensity. These observations are attributed to strong rotational dependencies of the specific dissociation rate constants k(E,J) and to CO2 laser-intensity-dependent rotational distributions of the excited CF3I. The corresponding rotational distributions are reconstructed from the observed experimental time profiles of the reaction rates. In addition to the detection of the I(2P3/2) dissociation product from infrared multiphoton excitation, populations of vibrationally highly excited CF3I* were identified via electronic excitation in the visible, subsequent fast dissociation and REMPI detection of the resulting I(2P1/2). At weak IR laser intensities these vibrational distributions were found to be strongly bimodal. However, the bimodal character weakens with increasing laser intensity, tending towards a single broad distribution at very high laser intensities.

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