Ultraviolet absorption cross sections of infrared laser excited UF6

Abstract

Ultraviolet absorption cross sections of ν3 vibration-excited UF6 molecules were measured in the wavelength region between 230 and 280 nm. The state-selective excitation was accomplished by 16 μm laser pumping of the ground vibrational state of flow-cooled UF6. Maximum changes in the absorption cross sections were observed toward longer wavelengths in the wings of the two charge transfer bands located at 220 and 260 nm. The results are discussed in terms of a transition from the ν3 vibrationally excited state to an upper dissociative potential surface. The change in the UV absorption cross section was also monitored as a function of the IR laser frequency and the sample gas temperature. The IR excitation spectrum follows qualitatively the low resolution contour of the ν3 Q branch. The magnitude in the absorption change is dependent on the fraction of molecules being accessed by the IR laser. The characteristic relaxation time for the ν3 excitation was estimated to be about 0.25 μs Torr at 100 K.