Absorption spectra of C6H6 and C6D6 near 340 nm

The absorption spectra of C₆H₆ and C₆D₆ in the liquid phase have been studied near 340 nm. The absorption spectrophotometric mounting was a sequential double-beam attachment with linear response to energy on scanning of the spectrum before the exit slit and an electronic device which gives directly either the absorbance or the integrated absorbance of a transition and, consequently, its oscillator strength.The oscillator strength measured for the band of C₆H₆ is 8×10^?8, which corresponds to a dipole moment of 2.4×10^?3 Debye; this value is of the same order as a theoretical value calculated by Tsubomura and Mulliken (3.8×10^?3 Debye) for a transition between states ³F and ³A of an oxygen-benzene pair. This agreement corroborates the hypothetical existence of such a transition.The first vibrational band is at 28553 cm^?1 for C₆H₆; this band is not observed in the vapor or solid phase. It corresponds probably to the transition 0-0, which is considered in the literature to be near 29500 cm^?1. The isotopic shift measured for this first band is 164 cm^?1. The vibrational frequencies are, respectively, 910 cm^?1 for C₆H₆ and 889 cm^?1 for C₆D₆.