Radiative and nonradiative transitions in the first excited singlet state of simple linear aldehydes

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Abstract
Radiative and nonradiative rates of asymmetric linear aldehydes (C2∼C6) have been measured in the gas phase. Observe radiative lifetimes are compared to calculated radiative lifetimes obtained from the Strickler–Berg (SB) expression. The calculated values are about the same as the observed values in large aldehydes, but the former is about six times greater than the latter in acetaldehyde. The radiative rates are about four orders of magnitude smaller than the nonradiative rates. The two most important nonradiative processes are S1→T1 intersystem crossing and type II processes, the latter playing an increasingly important role at high energy in the aldehydes with γ‐hydrogens. The contrasting radiative behavior of the asymmetric aldehydes from that of the symmetrical ketones is intriguing and suggests important differences in their excited state equilibrium geometries and transition moments.