Accurate quantum yields by laser gain vs absorption spectroscopy: Investigation of Br/Br* channels in photofragmentation of Br2 and IBr

A two-laser pulse-and-probe technique is used to study photofragmentation of Br2 and IBr over the wavelength range 450–530 nm. The metastable Br(2P1/2–2P3/2) transition is probed by time–resolved laser gain vs absorption spectroscopy using a tunable color center laser. This new approach to the measurement of quantum yields provides highly accurate absolute values for Br*(2P1/2) production. The peak quantum yield for Br2 photodissociation is φ=87% at λ=500 nm. The difference between the spectral variation of φ and the total absorption spectrum characterizes the A state of bromine, which contributes ≲14% to the absorption spectrum at λ=510 nm. The peak in the Br* yield from photofragmentation of IBr is φ∼73% at λ=500 nm. The present absolute IBr data together with the previous molecular beam studies suggest a reassessment of the contributions of the continuum states in IBr. The laser gain vs absorption method for obtaining quantum yields is readily generalized to other atoms and molecules.

Accurate quantum yields by laser gain vs absorption spectroscopy: Investigation of Br/Br* channels in photofragmentation of Br2 and IBr Journal Articles