Pressure dependence of fluorescence quantum yields and collision-induced rotational relaxation of single rotational levels of H2CO(<i>A</i> 1<i>A</i>2, 41)

Abstract

Pressure dependent values of SRL fluorescence quantum yields Φf(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 Φf 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 Φf(J′, K′).