Pressure and composition dependences of acetone laser-induced fluorescencewith excitation at 248, 266, and 308 nm

In previous studies, acetone has been successfully applied as a tracer for planar laser-induced fluorescence (PLIF) measurements of concentration and temperature. The desire to extend acetone PLIF capability to conditions of varying pressure and composition has motivated studies of the effects of th ese quantities on fluorescence yield. The present work explores pressure an d composition effects over a 0.5 to 16 atm range for the three excitation w avelengths of greatest interest for diagnostics: 248, 266, and 308 nm. In a ccord with previous studies, fluorescence per acetone molecule is seen to i ncrease with pressure, apparently towards a high-pressure limit for each wa velength, with the most significant effect observed at short wavelengths. B ath gas composition is also seen to affect fluorescence intensity, with an impact related to the effectiveness of the bath gas species at vibrationall y relaxing excited acetone. A model of fluorescence yield considering the r elative rates of intersystem crossing and vibrational relaxation for excite d singlet acetone describes the measured pressure and composition dependenc es well. To explain an oxygen fluorescence quenching effect that is observe d experimentally, a term is added to the model to represent oxygen-assisted intersystem crossing. The data and model results provide useful guidance f or diagnostic applications. A key conclusion is that long excitation wavele ngths are preferable from the standpoint of minimizing pressure and composi tion dependences.