Experimental study of the higher π→π^* transitions of benzene in low-temperature matrices

In this paper we present the results of an experimental study of the absorption spectrum of benzene and deuterated benzenes in solid Ar, Kr, Xe, and N₂ in the spectral region 2800-1700 Å, with special reference to the 2100- and to the 1850-Å transitions. Our main results are: (a) On the basis of the observed vibrational structure the second excited singlet state of the benzene molecule is assigned to the ¹A₁₂- →¹B_1v rather than to the ¹A _1g→¹E_2g excitation. (b) Theoretical calculations of the dynamic electronic-vibrational coupling between the ¹B_1x and the ¹E_1u states support the ¹B_1x assignment of the 2100-Å transition. (c) The vibrational structure of the 1850-Å ¹A_1g→ ¹E_1u transition was resolved. (d) No experimental evidence for Jahn-Teller coupling in the π→π^{* 1}E _1u state was observed, in agreement with theoretical analysis. (e) Information on site splittings for the higher π→π^* excitation of benzene in rare-gas solids has accumulated. (f) Analysis of matrix shifts for the ¹A_1g→¹B_1u and ¹A_1g→¹E_1u transitions indicates that the "solvent effect" is dominated by dispersion interactions. (g) Information on deuteration effects on the ¹B_1u and ¹E_1u energy levels was obtained. (h) Qualitative information on intramolecular radiationless decay in the two higher π→π^* excited states of the benzene molecule has been inferred from the linewidths in the absorption spectrum.