Analysis of the naphthalene vapour absorption bands at 3200Å. I. Naphthalene h -8

Abstract

The absorption bands of naphthalene vapour near 3200 A have been measured at medium and high resolution and analyzed for the first time. The bands have strong heads weakly degraded to the red. The direction of polarization of the 0—0 pure electronic transition has been identified from the band contour of the corresponding band, which shows a single intense maximum. Calculations of rotational energy levels confirm that this is a quasi-parallel A -type band of the asymmetric rotor, with polarization along the longer in-plane molecular axis. Accompanying the electronically allowed band is a set of stronger vibrationally induced bands, which show doubled intensity maxima. From approximate calculations of contours it is confirmed that these are quasi-perpendicular B -type bands, polarized along the shorter in-plane axis. The electronic assignment B 2u <- A g , long-axis polarized, agrees with McClure’s assignment from the spectrum of naphthalene embedded in durene crystals. The use of rotational band contours for assigning transitions is novel in larger molecules and seems likely to be applicable rather widely. A hitherto unrecorded ground-state frequency 506 cm<super>-1</super> of species b 3g has been identified, and a number of other ground and excited-state frequencies confirmed and assigned, or recorded for the first time.