TEMPERATURE AND PRESSURE DEPENDENCES OF THE LASER-INDUCED FLUORESCENCE OF GAS-PHASE ACETONE AND 3-PENTANONE

Laser-Induced Fluorescence (LIF) from the S-1 state of acetone and 3-p entanone was studied as a function of temperature and pressure using e xcitation at 248 nm. Additionally, LIF of 3-pentanone was investigated using 277 and 312 nm excitation. Added gases were synthetic air, O-2, and N-2 respectively, in the range 0-50 bar. At 383 K and for excitat ion at 248 nm, all the chosen collision partners gave an initial enhan cement in fluorescence intensity with added gas pressure. Thereafter, the signal intensity remained constant for N-2 but decreased markedly for O-2. For Synthetic air, only a small decrease occurred beyond 25 b ar. At longer excitation wavelengths (277 and 312 nm), the correspondi ng initial rise in signal with synthetic air pressure was less than th at for 248 nm. The temperature dependence of the fluorescence intensit y was determined in the range 383-640 K at a constant pressure of 1 ba r synthetic air. For 248 nm excitation, a marked fall in the fluoresce nce signal was observed, whereas for 277 nm excitation the correspondi ng decrease was only half as strong. By contrast, exciting 3-pentanone at 312 nm, the signal intensity increased markedly in the same temper ature range. These results are consistent with the observation of a re d shift of the absorption spectra (approximate to 9 nm) over this temp erature range. Essentially, the same temperature dependence was obtain ed at 10 and 20 bar pressure of synthetic air. It is demonstrated that temperatures can be determined from the relative fluorescence intensi ties following excitation of 3-pentanone at 248 and 312 nm, respective ly. This new approach could be of interest as a non-intrusive thermome try method, e.g., for the compression phase in combustion engines.