VAPOUR PHASE TWO PHOTON PHOTOACOUSTIC SPECTROSCOPY OF $ACETONE^{*}$

* Supported by National Science Foundation. $\dagger$ Taken from the doctoral thesis of D. Guo to be submitted to Rutgers University (1992).Author Institution: Chemistry Department, Rutgers UniversityTwo-photon photoacoustic spectra of acetone-$h_{6}$ and -$d_{6}$ have been recorded for the first time using a high flux injection seeded pulsed laser in the wavelength region 667 to 677nm. Systematic studies have been carried out to observe the effects of photoacoustic saturation on the vibronic transitions as a function of laser power and the microphone and excitation region separation. Comparison of the two-photon acetone photoacoustic multiphoton ionization spectra shows intensity reversal between the $^{1}A_{2} \leftarrow ^{1}A_{1}$ and $^{1}A_{1} \leftarrow^{1}A_{1}$ transition origins. The intensity reversal indicates different rates of nonradiative relaxations from the two excited states which in turn suggests that these two ``Rydberg States"" posses different character