Gas-phase luminescence of aromatic carbonyl compounds in excited nitrogen at atmospheric pressure

Abstract

Certain types of aroyl compounds such as benzaldehyde, acetophenone, benzophenone, and anthraquinone produce intense gas-phase luminescence in excited nitrogen at atmospheric pressure. This luminescence was measured in pressure ranges of 1.00–1.67 atm and temperature ranges of 343–473 K. A novel, radioactively (Ni-63) stimulated, high-voltage( [Formula: see text]1750 V/mm), low-current ( [Formula: see text]35 nA) discharge in high-purity nitrogen was used for gas chromatographic detection and spectral excitation. The gas-phase luminescence spectra of about sixty aroyl compounds - introduced as gas chromatographic peaks - could thus be measured and compared with literature spectra obtained by conventional excitation in condensed phases. Only a few gas-phase spectra are available from the literature, and these did agree well with the spectra of this study. A speculative luminescence mechanism is proposed, in which ground-state N2 becomes excited by collision with fast electrons. This is followed by efficient triplet-triplet energy transfer from N2(A 3Σu+) to the n–>π* excited aroyl compound. Key words: aroyl phosphorescence, excited-nitrogen excitation, aroyl triplet-triplet excitation, aroyl luminescence detection, gas-phase phosphorescence spectra, gas-phase aroyl detection.