Low lying 1A2u(σ,π*) and 1E2g(π,π*) states of benzene as suggested by Raman intensities

Abstract

The Raman spectra of benzene, substituted benzenes, and charge transfer complexes between benzene and halogens were observed. The great preresonance intensity enhancement of the out‐of‐plane ν₁₀(e_1g) Raman line of benzene and its intensification upon the complex formation strongly suggest the existence of the low lying ¹A_2u(σ,π*) state of benzene. On the other hand, the preresonance Raman effect of the overtone of the ν₁₄(b_2u) vibration of benzene and the strong appearance of Raman and infrared inactive fundamentals ν₁₆(e_2u) and ν₁₇(e_2u) of benzene upon the complex formation can be explained by assuming the low lying ¹E_2g(π,π*) states. It is qualitatively concluded that the perturbation imposed on benzene in the direction perpendicular to the molecular plane induces the intensity enhancements of the out‐of‐plane vibrations, while the perturbation parallel to the molecular plane contributes greatly to the Raman intensities of the in‐plane modes.