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Modification of a Commercial Spectrophotometer for Photoacoustic Measurement

Volume 37, Number 6 (Dec. 1983) Page 564-565

Bandyopadhyay, S.; Harris, J.M.; Eyring, E.M.

Photoacoustic spectroscopy (PAS) is an established technique for optical spectroscopic study of chemisorbed species on surfaces of highly absorbing or highly scattering condensed phase samples in the UV, VIS, and IR region. The technique typically involves enclosing the sample in a sealed cell containing a transparent gas which is also in contact with the diaphragm of a sensitive microphone. Intensity-modulated monochromatic light is directed onto the sample through a window in the cell. If the light is absorbed by the sample, subsequent nonradiative relaxation of the molecules at the sample surface will give rise to thermal fluctuations within the sample. When these thermal waves reach the sample/gas interface, heating and expansion of the thin layer of gas adjacent to the sample surface generates pressure fluctuation within the gas of the same frequency as the intensity modulation of the incident light. The acoustic waves are monitored by the microphone. As the wavelength of the light is continuously varied, a spectrum of the sample similar to an absorption spectrum is produced if the intensity of the acoustic wave is plotted vs wavelength of light.