The infrared spectrum of benzene in a solid HCl “matrix”

Abstract

Studies are presented of the infrared absorption spectrum of benzene in an HCl “matrix” (HCl :benzene mole ratio of about 10:1). These results are compared in both frequency and intensity with the spectrum of crystalline benzene and of “glassy” benzene. The pathlengths needed to obtain the intensities of these thin solid films have been measured by observing interference fringes at a fixed wavelength as the film is deposited. In general, the spectra in all these phases (crystal benzene, “glassy” benzene, and complexed benzene) are similar. Splittings observed in the crystal disappear in the other two phases; otherwise frequencies are quite similar. A number of absorption bands, forbidden in the spectrum of the pure crystal, appear weakly in the “glass” and/or in the spectrum of benzene in the matrix. Also the intensity of the gas-phase allowed fundamentals ν 18 and ν 20, show a surprising decrease in the HCl matrix. The quantitative comparison of these relatively small changes observed in the spectrum of benzene in these different phases suggests benzene in the HCl matrix is in a site of approximately D 6 h symmetry, but is strongly perturbed.