Pulsed technique for observing infrared emissions from ionic gas phase reactions at low reactant ion concentrations
. Rev Sci Instrum 2000
A technique has been developed to detect infrared emissions from the products of ionic reactions in plasmas. The technique employs dual-phase digital lock-in amplification and cold filtering to permit the detection of the weak infrared chemiluminescence (IRCL) with a solid-state detector. A novel method of cleanly modulating plasma chemiluminescence by the pulsed introduction of reagent gases has been developed and implemented. This new technique has been tested by studying the well-characterized H-atom reactions, H+Cl-2-->HCl(v=0-4)+Cl and H+NO2-->OH(v=0-3)+NO. Rotational and vibrational distributions have been measured for these two reactions and are presented and compared with previous determinations. Additionally, the associative electron detachment reaction, H+Cl--->HCl(v=0-2)+e, has been studied, demonstrating that IRCL can be collected from reactions occurring at a low number density approaching that of the plasma ionization (similar to 4x10(10) cm(-3)). The resolution, and hence, the information content of the collected emissions from this reaction have been greatly improved over previous work, with which our data are compared. (C) 2000 American Institute of Physics. [S0034-6748(00)04904-2].