Synchrotron infrared photoacoustic spectroscopy

The use of synchrotron radiation (SR) as a far- and mid-infrared source in the measurement of photoacoustic Fourier transform infrared spectra of soli ds is demonstrated for the first time in this work. Initial experiments wer e performed at beamline U10A at the National Synchrotron Light Source, Broo khaven National Laboratory. For synchrotron photoacoustic spectroscopy to b e feasible, it must yield results superior to those obtained with a convent ional thermal (Globar(R)) source; accordingly, SR and Globar(R) photoacoust ic spectra recorded under similar conditions were compared in detail. The i ntensities of SR far-infrared photoacoustic spectra were found to be consis tently greater than the corresponding Globar(R) spectra. At shorter wavelen gths, SR always underfills the effective aperture (or, alternately, sample size); SR is a superior source in a spectral region that is a function of t his aperture. The high wave number limit of this region exhibits a power-la w dependence on aperture size. This investigation also showed that the enti re mid-infrared photoacoustic spectrum is more intense using SR and apertur es smaller than approximately 0.5 mm. (C) 2001 American Institute of Physic s.