Pressure dependence of fluorescence quantum yields and collision-induced rotational relaxation of single rotational levels of H2CO(Ã 1A2, 41)

Abstract

Pressure dependent values of SRL fluorescence quantum yields Φ_f(J′, K′) in the 1–120 mTorr range are reported for 75 rotational levels (E^′_rot = 37–1127 cm⁻¹) of S₁ H₂CO (4¹). High lying rotational levels tend to show an increase in Φ_f with increasing pressure of S₀ H₂CO, whereas low lying rotational levels tend to show a decrease. For some levels, collision‐induced ΔJ′ transitions occur 5–10 times faster than the gas kinetic collision rate but probably with a much slower rate for ΔK′ transitions. A ΔK′‐constrained, collision‐induced rotational relaxation model involving mainly ΔJ′ = ±1 transitions is proposed to explain the observed pressure dependence of Φ_f(J′, K′).