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 2800–1800 Å. 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 A1g1 → B1u1 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 E1u1 state of the benzene molecule.