We present a first measurement of the absorption profile of the eighth harmonic of the C–H stretch in liquid benzene using a recently developed optoacoustic absorption measurement technique involving a pulsed dye laser and submersed piezoelectric transducer. The absorption maximum occurs at 21 040±7cm−1, with a peak absorption coefficient of (9.2±1.5) ×10−5 cm−1. The full linewidth of the absorption profile is 354±9cm−1. We have previously reported similar measurements for the sixth and seventh harmonics. We have also obtained spectra of lower harmonics by conventional spectrophotometry. We make a comparative survey of the studies of this series of overtone absorptions. With our accurate determination of the nth harmonic absorption for large n, we propose an improved anharmonic formula to fit the experimental peak positions. We also note that the absorption linewidth increases linearly with n in liquid benzene.
We use the recently developed technique of pulsed dye-laser optoacoustic spectroscopy of liquids to study the weak 607-nm absorption band of benzene dissolved in various concentrations in CCl(4). The technique involves the use of submersed piezoelectric transducer and gated detection of the transient acoustic signal. With increasing dilution, the peak of the 607-nm band is observed to be more blue-shifted, and the linewidth and asymmetry of the band decrease. We verify that the present technique can detect absorption coefficients of 10(-6) cm(-1) and absorbed energy of 10(-9) J. With these high sensitivities, we show that nonlinear optical processes such as multiphoton absorption and stimulated Raman scattering in liquids should be readily observable with our optoacoustic method.
We report a novel optoacoustic (OA) cell construction which has improved small absorption measurement capability from 10−9 cm−1 to 10−10 cm−1. The new OA cell is ideally suitable for use with planar output lasers, e.g., diode lasers. Now optoacoustic spectroscopy can be extended to include the effects of low temperatures, electric fields, and magnetic field effects.
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