Fluorescence and radiationless decay pathways of dimethyldiazirine (S 1) in the gas phase

Abstract

Fluorescence emission was observed from dimethyldiazirine (DMD) excited at 350–360 nm, and the fluorescence excitation spectrum was obtained in the gas phase. The emitting state was identified as the first excited singlet state, S 1( 1B 2), based on the dispersed fluorescence spectrum and a comparison of the excitation spectrum with the absorption spectrum reported previously. The S 1 state efficiently decayed through radiationless processes. An analysis of the relative decay rates, deduced from the intensity ratios of the fluorescence excitation and photoacoustic spectra, led to the conclusion that DMD in the S 1 state decays via two radiationless decay pathways: one was energy dependent with a barrier of 300±50 cm −1 and the other was almost energy independent. The former was attributed to vibrational predissociation to dimethylcarbene and N 2, and the latter to internal conversion to highly vibrationally excited levels of S 0. The fluorescence quantum yield was estimated to be 0.002 or less at the electronic origin of the S 1 state.