Abstract

A novel technique was used to measure the photodissociation cross section of Pb₂. This technique has the important advantage that the Pb₂ density need not be known. An excimer laser (XeCI) operating at 308 nm photodissociated the Pb₂, while a single-mode argon-ion laser probed the ground state dimer absorption at 496.5 nm. The Pb₂ was produced in a heat pipe at ~1300°C. A similar technique was described by Kwong et al.¹ and applied to atomic transition probability measurements; however, their approach requires a measurement of the ground state atomic density. The technique reported in this paper makes use of the fact that the laser-induced change in the ground state Pb₂ density depends only on the fluence of the dissociating laser and the photodissociation cross section. Consequently, from a measurement of the relative change in the density as a function of fluence, the cross section may be deduced. The above analysis is valid in the approximation that the molecular vapor is optically thin at the frequency of the dissociating laser. The widespread availability of excimer lasers with emission into the vacuum ultraviolet should make this technique readily applicable to the measurement of absolute photoionization and photodissociation cross sections.

© 1985 Optical Society of America