Electronic Spectra of Some Methyl Substituted Benzenes in a Rare-Gas Solid

Abstract

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) $\mathrm{\pi \hspace{0.17em}\to \hspace{0.17em}\pi *}$ 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) $\mathrm{\pi \hspace{0.17em}\to \hspace{0.17em}\pi *}$ transition is consistent with the ${}^1{A}_{\text{1g}}{\mathrm{\hspace{0.17em}\to \hspace{0.17em}}}^1{B}_{\text{1u}}$ assignment for this transition in the benzene molecule. (c) The vibrational structure of the third (1850 Å) $\mathrm{\pi \hspace{0.17em}\to \hspace{0.17em}\pi *}$ 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 ${}^1{E}_{\text{1u}}$ state of the benzene molecule.