Infrared spectra of benzene in solid argon

Highly isolated benzene molecules with near zero matrix shift have been prepared in the argon matrix at 9 K. By correlating the peak frequencies in the matrix state with those in other states, uncertainties could be resolved for the Fermi triad in the C-H stretching region of gas phase spectrum. The gas phase frequencies inferred from the matrix data were found in good agreement with those from the supersonic jet experiment. Based on the concentration and the temperature dependence, the peaks in the matrix spectra were classified in terms of monomeric, dimeric, and multimeric species.