The rotatory dispersion of benzil

Abstract

The paper reports a study of the rotatory dispersion and the ultraviolet absorption spectrum of crystalline benzil. Transmission spectra have been photographed with varying thicknesses of the crystal. Even with the thinnest specimens (0.02 mm.) there is an almost complete cut off in the transmitted intensity beyond 3400 Å marking the presence of an intense absorption band farther out in the ultraviolet. There is another comparatively feeble absorption which extends from 4500 Å onwards into the shorter wavelength region of the spectrum with a maximum at, 3900 Å. This band is markedly pleohroic. The rotatory dispersion has been measured from 9000 Å in the infrared upto 3600 Å in the ultraviolet right through the absorption band. A specimen of 0.03 mm. thick had to be used in order to penetrate the band. The crystal exhibits anomalous rotatory dispersion in the region of absorption. The one-term rotatory dispersion formula ρ²=6.27 λ²/[λ²-(0.24)²]² fits the data quite well except in the immediate vicinity of the absorption band. The temperature variation of the rotatory power has been measured for three wavelengths in the visible.