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

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, k_eff=kN₂–M +0.914(XCO₂/XN₂) kCO₂–M, has been determined for XCO₂/XN₂=0.071 and M = Li, Na, K, and Cs: Li, k_eff=1500±500 torr⁻¹ · sec⁻¹; Na, k_eff=1400±200; K, k_eff=4600±1000; Cs, k_eff=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.