High overtones of C–H stretch in liquid benzene measured by laser optoacoustic spectroscopy

Abstract

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.