Pressure and composition dependences of acetone laser-induced fluorescence with 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 these quantities on fluorescence yield. The present work explores pressure and composition effects over a 0.5 to 16 atm range for the three excitation wavelengths of greatest interest for diagnostics: 248, 266, and 308 nm. In accord with previous studies, fluorescence per acetone molecule is seen to increase with pressure, apparently towards a high-pressure limit for each wavelength, with the most significant effect observed at short wavelengths. Bath gas composition is also seen to affect fluorescence intensity, with an impact related to the effectiveness of the bath gas species at vibrationally relaxing excited acetone. A model of fluorescence yield considering the relative rates of intersystem crossing and vibrational relaxation for excited singlet acetone describes the measured pressure and composition dependences well. To explain an oxygen fluorescence quenching effect that is observed experimentally, a term is added to the model to represent oxygen-assisted intersystem crossing. The data and model results provide useful guidance for diagnostic applications. A key conclusion is that long excitation wavelengths are preferable from the standpoint of minimizing pressure and composition dependences.