Radiative Lifetimes of Argon Molecules and Dependence on Internuclear Distance

Time-resolved fluorescence studies of Ar₂ formed by supersonic jet expansion and excited by monochromatic, tunable, vacuum-ultraviolet radiation have been used to measure the radiative lifetimes of selected high vibronic levels of the A1ᵤ state. Lifetimes of levels v^'=24 to 30 were found to have an average value of 160 ±{} 10 ns. This differs by a factor of {~} 20 from the lifetime of 2.88 ±{} 0.06 {μ}s obtained earlier for the v^'~0 level with high gas pressures and excitation by charged particles. It is shown that this large difference in lifetimes arises from a sixfold increase in the electronic transition moment for a change of internuclear distance from 2.5 to 3.5 {}.