Hydrogen atom sources for electrically pulsed hydrogen halide lasers

Abstract

With the aim of optimizing the performance of electrical discharge pulsed high-pressure hydrogen halide lasers, we have investigated the effects of over forty chemicals on these systems. We have examined those compounds for which the chain carrying step, X + HR \underrightarrow{(1)} RX + H (X = Br, Cl, or F) promised to be more exothermic than the corresponding step with the usual fuels (i.e., R = H or a simple hydrocarbon radical). In the case of the less reactive halogens, production of hydrogen atoms in a nonchain reaction, directly initiated by the discharge, may well compete or dominate reaction (1) on the time scale of the lasing pulse. Because of this and the low electron temperature associated with high pressure discharges in electronegative gases, we have examined chemicals that contain a weakly bound hydrogen or a weakly bound, but highly reactive radical that could react in a second step to yield hydrogen atoms. These could then react in the lasing step, H + XR' → HX + R', to give vibrationally excited HX. Chemicals used included H 2 S, H 2 O 2 , highly chlorinated alkanes, alkines, and aldehydes, hydrazine, silane, and several substituted derivatives thereof. Helium and argon which improve discharge characteristics were also studied. The reaction was initiated by a 30-kV electric discharge from an array of needle electrodes, each resistively ballasted. The halogen sources used were the usual Br 2 , Cl 2 , and SF 6 . Results such as the enhancement of HBr lasing in a H 2 + Br 2 mixture upon the addition of O 2 but not upon the addition of N 2 can only be explained in terms of the ensuing chemical reactions and will be discussed.