Wavelength dependence of the photoassociation of Kr(4p^{6 1}S₀)-F(2p^{5 2}P) collision pairs

The excitation spectrum for the photoassociation (bound←free absorption) of thermalized pairs of Kr(4p^{6 1}S₀) and F(2p^{5 2}P) atoms in Kr/F₂ gas mixtures at 300 K has been recorded in the ultraviolet (208≤λ≤250 nm). By photodissociating F₂ in the presence of Kr and subsequently photoexciting Kr-F collision pairs in the ground state thermal continuum with tunable laser radiation, deeply modulated Franck-Condon structure associated with bound←free transitions terminating on the lowest 26 vibrational levels of the B ²Σ ion pair state of the KrF molecule was observed. Since the KrF ground state interaction potential is repulsive, photoassociation occurs in a narrow (ΔR≈0.7 Å) Franck-Condon region and structural information regarding the upper and lower state potentials, as well as the dependence of the electronic transition moment on internuclear separation, can be extracted from the spectrum. The Kr-F system is presented here as an example of the effectiveness of photoassociation as a tool with which one can determine the chemical, structural and optical properties of small excimer molecules that are otherwise difficult to access experimentally.