The vibrational structure of the electronic spectra of quinoxaline in shpolskii-type hydrocarbon matrices

Quasilinear spectrum of the S₁(n, π¹, ¹B₁) ← S₀ transition of quinoxaline in crystalline methylcyclohexane matrix and quasilinear phosphorescence spectra of quinoxaline in high- and low-temperature modifications of isooctane matrix were obtained at 77 K. The results of a full vibrational analysis of the spectra are presented and discussed. The diffuseness of the absorption spectrum in the range 3200-2900 Å is ascribed essentially to a small energy gap between the S₂ and S₃ states. The activity of out-of-plane vibration, 865 cm^-1, in the phosphorescence and the influence of matrices on the structure of the spectra suggest the possibility of out-of-plane distortion of the quinoxaline molecule in the T₁ state.