Vapor Absorption Spectra of Light and Heavy Naphthalenes at 2900—2500 A

The 2900—2500 A region of absorption in both light and heavy naphthalene is interpreted as an allowed A1g–B2u transition, and the bands at 35 910 and 36 040 cm—1 are assigned as the respective 0,0 bands. Upper-state frequencies of 485, 710, 995, 1390, 1520, and 1600 cm—1 and the ground-state frequencies of 495, 755, 1024, and 1380 cm—1 in the ordinary naphthalene spectrum are correlated with previously reported Raman frequencies. A corresponding interpretation is given for the vibrational frequencies occurring in the spectrum of deuterated naphthalene. The general appearance of the spectrum is compared with recent absorption curves in solid solution by Passerini and Ross, and with crystal data obtained with polarized light. Possible occurrence of vibrationally induced ``forbidden'' bands is discussed.