High resolution absorption studies of the b1Πu ← X1Σg+ system of nitrogen

Abstract

New high resolution studies of the absorption spectrum of N2 have been made in the region 1015–795 Å. Analyses are given of 25 non-Rydberg bands of the type 1Πu–X1Σg+. It is shown that all of these bands, which include the i, j, b, l, m, p, and q groups of Worley, together with several new bands not previously observed, can be assigned to a single transition the upper state of which is called b1Πu. The pronounced irregularities in the vibrational and rotational structure of the b state are attributed to a homogeneous interaction with the first member (n = 3) of the ---(3σg) npπu, 1Πu Rydberg series. This perturbation is discussed in the accompanying paper by Dressier who recognized its importance in the interpretation of the spectrum. Diffuseness in the rotational lines of several bands at lower ν was observed and is attributed to predissociation by a triplet state, probably the C′ 3Πu state which goes to the 4S + 2D dissociation limit. Three levels of the b state show measurable Λ-type doubling which can be interpreted as caused by interaction with vibrational levels of the first member (n = 4) of the --(3σg) npσu, 1Σu+ Rydberg series. The assignment of 28 non-Rydberg 1Σu+ levels, including the b′, g, f, r, s, and t "states", to a single 1Σu+ state which is called b′, is also briefly discussed.