Spectroscopic Studies in the Near Ultraviolet of the Three Isomeric Dimethylbenzene Vapors. I. Absorption and Fluorescence Spectra of Para-Dimethylbenzene

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Abstract
The absorption spectrum of para-xylene between 2850 and 2350A was photographed using a 3-meter grating spectrograph, and the corresponding fluorescence spectrum between 3125 and 2720A was photographed with a Bausch and Lomb medium quartz spectrograph. The electronic transition involved is interpreted as 1A1g—1B3u with the 0, 0 band at 36733 cm−1. Progressions in the fluorescence spectrum involve the totally symmetric vibrations 829 and 1208 cm−1, while progressions of the corresponding frequencies 775 and 1185 cm−1 appear in the absorption spectrum. A weak portion of the spectrum is identified with a so-called forbidden transition involving the β1g-component of the 606εg+ benzene vibration. This β1g-vibration has a frequency of 648 cm−1 in the ground state and of 552 cm−1 in the upper state. The α1g-component of the εg+ benzene vibration in para-xylene has a lower state frequency of 458 cm−1 and the upper state value of 367 cm−1. The Tesla luminescence spectrum is interpreted in relation to the fluorescence and absorption spectra.