The electronic absorption and vibrational spectra of 2,6-and 3,5-dichlorobenzonitriles

Department of Physics, University of Gorakhpur, Gorakhpur 273001, U.P., India.

Abstract

The electronic absorption spectra of 2.6- and 3,5-dichlorobenzonitriles have been photographed in vapour phase on medium quartz spectrograph. The observed spectra correspond to A_1g → B_2u transition of benzene. The 0,0 band of the observed absorption systems for 2,6- and 3,5-dichlorobenzo- nitriles have been identified at 34 015 and 34 262 cm^-1 respectively. Best of the bands were assigned as ground and excited state fundamentals, their combinations and overtones. In the case of 2,6-dichlorobenzonitrile the shorter wavelength band system corresponding to A_1g → B_1u transition of benzene has also appeared. The infrared absorption spectra of these mole- cules have also been studied in the region (200-4 000 cm^-1). The assigned ground and excited state fundamentals from ultraviolet absorption spectra have been correlated with infrared data.

Résumé

Spectres électroniques en phase gazeuse (spectrographe à prisme de quartz) des dichloro 2,6- et dichloro 3,5-benzonitriles. Ils correspondent aux transitions A_1g → B_2u du benzène. Les bandes O — O ont été identifiées à 34 015 cm^-1 et 31 262 cm ^-1 (isomères 2 ,6 et 3,5). Attribution des autres bandes fondamentales, combinaisons et harmoniques des états fondamental et excité. Pour le dichloro 2,6-benzonitrile on observe aussi le système de bandes aux faibles longueurs d’ondes correspondant à la transition A_1g → B_2u. Étude de l'absorption IR entre 200 et 4 000 cm^-1, corrélation entre les données IR et les fondamentales observées en UV.