Photodissociation dynamics of CF3I investigated by two-color femtosecond laser pulses

摘要

We report an experimental study of the multiphoton dissociation dynamics of CF3I performed on a home-built femtosecond laser pump-probe system; with time-of-flight mass spectrometer. The first repulsive A band and the 5p pi(3)7s sigma v(2) = 1 Rydberg state of CF3I were accessed by one- and two-photon transitions at 267 nm, respectively; with the latter two-photon absorption followed by a further two-photon probe transition at 401 nm to the (B) over tilde state of the parent ion. The observed signals from the CF3+ and I+ fragments show similar multi-component exponential decay patterns but the former is 4 times stronger than the latter. However; the parent CF3I+ signal was observed to evolve in a very different manner; decreasing sharply when probed in the first 289 fs following excitation and subsequently rising again after 860 fs to a constant level below that measured at negative pump-probe delay times when the pump and probe pulses exchange roles. This dip observed in the parent ion profile; is very different from that previously reported at shorter pump wavelengths of 264 nm or 265 ran, and is interpreted as the competition between two different ionization channels. One from the vibrationally excited v(2) = 1 of the irradiated Rydberg state and the other from the dissociative vibrational origin of the same electronic state which is populated by internal vibrational relaxation.