Ultraviolet absorption and laser-induced fluorescence of shock-heated acetylene

Abstract

Acetylene as a major intermediate in fuel pyrolysis and combustion has so far mostly been ignored as a contributor to UV absorption and fluorescence. Temperature-dependent ultraviolet absorption cross-sections of acetylene (C2H2) have been studied behind reflected shock waves between 565 and 1500K. Light from a deuterium lamp was transmitted through shock-heated gas mixtures and transmission spectra were recorded with ∼50µs time resolution. The absorption spectra strongly depend on temperature and show a strong red-shift with temperature. Above 900K, significant absorption is observed at 266nm. Laser-induced fluorescence (LIF) spectra were recorded in the shock tube using 266-nm laser excitation. In accord with absorption experiments, no LIF signal is observed below 900K. Above, the fluorescence intensity increases and the fluorescence spectra become broader over the studied temperature range. From fluorescence intensity and absorption cross-sections, relative effective fluorescence quantum yields are determined as a function of temperature.