Electronic spectra of some methyl substituted benzenes in a rare-gas solid

In this paper we present the results of an experimental study of the absorption spectrum of toluene, toluene-d₈, para-xylene, and meta-xylene in solid krypton in the spectral region 2800-4-1800 A. Our main results are: (a) The absorption spectrum of the first (2700 Å) π→π* transition is very sharp for all these matrix isolated molecules and resembles in detail the gas-phase spectrum. (b) The observed vibrational structure of the second (2200 Å) π→π* transition is consistent with the ¹A₁₀→ ¹B_1u assignment for this transition in the benzene molecule. (c) The vibrational structure of the third (1850 Å) π→π* transition was resolved. An electronic splitting of 350 cm^-1 was observed in the third excited state of para-xylene, which results from lifting of the degeneracy of the corresponding ¹E _1u state of the benzene molecule.