Laser-induced atomic fragment fluorescence spectroscopy: A facile technique for molecular spectroscopy of spin-forbidden states
Abstract
Spectra of spin-forbidden and spin-allowed transitions in the mixed b3u ~ A1u+ state of Na2 are measured separately by two-photon excitation using a single tunable dye laser. The two-photon excitation produces Na*(3p) by photodissociation, which is easily and sensitively detected by atomic fluorescence. At low laser power, only the A1u+ state is excited, completely free of triplet excitation. At high laser power, photodissociation via the b3u triplet state intermediate becomes much more likely, effectively "switching" the observations from singlet spectroscopy to triplet spectroscopy with only minor apparatus changes. This technique of perturbation-assisted laser-induced atomic fragment fluorescence may therefore be especially useful as a general vehicle for investigating perturbation-related physics pertinent to the spin-forbidden states, as well as for studying allowed and forbidden states of other molecules.