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

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Abstract
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.

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