Chemiluminescent Reactions of He(23S) with Nitrogen, Oxygen, Carbon Monoxide, and Carbon Dioxide

Rate coefficients for chemiluminescent reactions of excited helium with N2, O2, CO, and CO2 were determined by measuring the spatial dependence of visible emission in a flowing helium afterglow apparatus at pressures between 1 and 2 mm Hg. Rate coefficients are approximately proportional to the temperature over the range 305°–527°K. The magnitudes extrapolated to 300°K in units of 10−10 cm3 molecule−1·sec−1 are as follows: N2 = 1.0 ± 0.3, O2 = 3.3 ± 0.9, CO = 1.7 ± 0.5, CO2 = 7.9 ± 2.5. The relative concentration of metastable He(23S) was determined by optical absorption measurements as a function of total flow rate (or pressure). A close correlation exists between the resulting curve and the curves for the total emission intensity. These data provide strong evidence that Penning ionization by He(23S) atoms is a major process for populating the emitting states.