High-Resolution Double-Resonance Spectroscopy of SF6

A good deal of effort has been devoted recently to understanding the collisionless multiphoton dissociation (CMPD) of CO2 laser-irradiated SF6 molecules. In the present work we have performed a double-resonance (DR) measurement by using a Q-switched CO2 laser to saturate a variety of υ3-mode transitions in a small volume of SF6 gas at low pressure, and probing that volume using the output of a tunable lead-salt diode laser. Our intent was to yield new insight into the assumed near-resonant excitation up the lower levels of the υ3 ladder by the CO2 laser, a process which, according to theory, is the first stage of CMPD and results in isotopic selectivity. The essential differences between our experiments and previous work [1,2] are that we used a continuously tunable probe source and that our collisionless DR signals, unlike those previously reported [1,2] were not likely the result of excitation into the molecular quasi-continuum.