Vibrational relaxation of N2 and CO2(001) by alkali metal atoms

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Abstract
A new technique, based on fluid modulation in a low‐pressure fast‐flow apparatus, has been used to measure the vibration‐to‐translation relaxation rates of N2 and CO2(001) by alkali metal atoms. Basically, the technique is to fluid‐modulate trace amounts of CO2 which are added to a fast‐flowing alkali metal‐active N2 mixture. The extremely fast resonant collisional exchange between N2(ν=1) and CO2(001) inverts the CO2(001) level, as in a fluid mixing laser, which is then probed with a CO2 laser. By measuring the optical gain with and without the alkali metal, the vibrational relaxation rates can be determined. This method enables gain changes as small as 0.1% to be measured. The effective rate, keff=kN2–M +0.914(XCO2/XN2) kCO2–M, has been determined for XCO2/XN2=0.071 and M = Li, Na, K, and Cs: Li, keff=1500±500 torr−1 · sec−1; Na, keff=1400±200; K, keff=4600±1000; Cs, keff=7900±2000. In the case of Na, XCO2 was also varied on order to determine the individual rates: kN2–Na=920±100 torr−1 · sec−1 and kCO2–Na=8100±2000 torr−1 · sec−1. These rates differ by orders of magnitude from theoretically predicted values.

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