3Π Levels and Predissociations of N2 near the 12.135-eV Dissociation Limit

Abstract

The two predissociations in the second positive bands, C ³Π_u→B ³Π_g, have been re‐examined in the light of recent spectroscopic studies of the N₂ spectrum. It is concluded that the predissociation of Büttenbender and Herzberg is due to a ⁵Π_u state and not to a ³Π_u state as formerly believed. However, a few details of the predissociation are not yet clearly explained. The second, less well‐known predissociation of Hori and Endo is interpreted as being in all probability due to the C′ ³Π_u state (the upper state of the Goldstein—Kaplan bands). This explanation requires that the C′ state have a maximum in its potential curve at an internuclear distance of about 2.0 Å. The behavior of the C and C′ potential curves, which should apparently intersect at about 1.4 Å, is interpreted as a noncrossing rule interaction. The vibrational structure in the region of the interaction is discussed and in particular the level reported by Pannetier et al. and that reported by Tanaka and Jursa are attributed to a mixture of v=5 of C and v=1 of C′. The level formerly tentatively assigned to v=1 of C′ is now considered to be primarily v=2 of the same state. Some low‐temperature afterglow mechanisms are discussed in terms of the new interpretations of the C and C′ states. The ⁵Π_u and ³Π_u states which are to be expected in the energy range of interest are discussed theoretically by the application of both the molecular orbital and the Heitler—London methods and the conclusions are found to be consistent with the present interpretation of the experimental results.