Infrared double resonance spectroscopy of V-T, R relaxation of HF(v=1): Direct measurement of the high-J populations

Abstract

The V‐T, R relaxation of HF(v=1) by HF is studied by infrared pulse‐probe transient absorption measurements using a tunable F‐center laser. It is found that a substantial fraction of the relaxation occurs through the high‐lying rotational levels of v=0. The results indicate that the states J=10–14 comprise ∼20%–40% of the population in the total relaxation, with the distribution increasing rapidly with decreasing J in this range. The observed signals, corrected for cascade, correspond to the fractions: J=10, ∼10%–40%; J=11, ∼4%–10%; J=12, ∼2%–6%; J=13, ∼1%–2%; and J=14, ∼0.05%–0.35%. In addition, the V‐T, R rate determined here, k=1.46±0.15×10⁻¹² cm³ molecule⁻¹ s⁻¹ reconfirms previous double resonance results. Also, studies involving buffer gas addition (Ar) give no indication of ‘‘bottleneck’’ effects on the high J’s. In fact, the R–R, T rates always exceed the V‐T, R rate by one to two orders of magnitude. For J=11–13, the R–R, T rates range from ∼1.2×10⁻¹⁰ to 6×10⁻¹¹ cm³ molecule⁻¹ s⁻¹.