Abstract
We describe a photoacoustic spectrometer optimized for the detection of nonradiative relaxation from molecular electronic states populated via two-photon excitation. The excitation source is a nitrogen-laser-pumped dye laser; the analog data-acquisition system automatically corrects the photoacoustic signal for pulse-to-pulse fluctuations in laser intensity; and the microcomputer interface is designed for universal communication to any microcomputer which supports an RS-232C I/O port. As an example of the capabilities of this spectrometer, we present two-photon photoacoustic spectra of CH3I and CD3I, covering small regions within the first s-Rydberg transitions, and show that the photoacoustic signal does indeed depend quadratically upon the incident laser intensity. These data represent the first direct detection of nonradiative decay from a molecular Rydberg state.
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