Photoacoustic Overtone Spectroscopy

The introduction of intracavity dye-laser photoacoustic detection inaugurated the, hitherto unexplored, area of gas-phase vibrational overtone molecular spectroscopy.1–3 We have used this technique to detect extremely weak overtone absorptions in more than 50 molecular systems in the spectral region 1000–400 nm. The molecular systems studied are: benzenes, halomethanes, propenes, and nitriles. Here, we present a summary of our recent work describing the photoacoustic techniques used to record the spectra, reduce the background window noise, optimize intracavity power, and measure absorption cross-sections. Also the characteristics of overtone transitions are reported.