Excitation and Dissociation Mechanisms in Molecules with Application to Mercuric Halide Laser System

摘要

Although the mercuric halide laser systems have received intensive study in recent years, being one of only two efficient electronic-transition lasers known, the precise collisional mechanisms leding to HgBr(B), formation and subsequent fluorescence are still imperfectly understood. The initial suggestion that direct collisional excitation of, say, HgBr sub 2 , by electrons (analogous to photoionization), i.e., HgBr sub 2 + e implies HgBr(b) + Br + e, was the dominant mechanism, was temporarily abandoned when a measurement by Allison and Zare yielded a cross section of only < 1 x 10 exp -20 cm exp 2 for low incident electron energy HgBr(B-x) fluorescence, much too small to explain the observed laser efficiency. Subsequent explanations for HgBr(B) formation included energy transfer from excited N sub 2 or rare gases, electronic recombination of HgBr sub 2+ , or dissociative electron attachment. Though it has recently been demonstrated that electronic energy transfer does play a role in HgBr(B) formation in the presence of N sub 2 or X/sub e/ buffers, modeling studies of e-beam sustained discharges have now conclusively shown that direct electron-impact excitation of mercuric halides, is indeed the dominant laser mechanism. The technique of electron-energy-loss spectroscopy was used to obtain pseudo-optical absorption spectra in HgBr sub 2 and HgCl sub 2 . Results are presented and discussed. (ERA citation 08:027038)