Transient gain-versus-absorption laser probing of spin-orbit states, kinetics and dynamics

Abstract

A tunable F-center laser and a diode laser are used to probe the spin-orbit populations of excited (2P1/2) and ground (2P3/2) state Br and I atoms at 2714 nm and 1315 nm, respectively. The technique uses pulsed laser photolysis and time-resolved cw laser probing of the gain or absorption signals from the coupled pair of states in the halogen atoms. Transient laser gain-versus-absorption measurements provide highly accurate quantum yields of the spin-orbit states in the photodissociation of molecules such as Br2, IBr, CH3I, ICN and C3F7I. In Br2, the continuum yields that result from absorption of vibrationally excited states are investigated as a function of temperature to determine the contributions to the absorption of individual upper excited states. The process of collisional dissociation upwards in energy, termed “collisional release”, is investigated with single vibronic state excitation. The high resolution of the probe lasers allows Doppler velocity effects to be studied, and differing reactivity of the spin-orbit excited and ground state atoms is explored. The high sensitivity and excellent time resolution of the transient gain vs. absorption technique provides a powerful way to study numerous kinetic phenomena with exceptional detail