Forbidden Absorption-Band Systems of N2 in the Vacuum-Ultraviolet Region

Abstract

Five systems of absorption bands of N₂, whose upper states are a ¹II_g, a′ ¹Σ_u^—, B′ ³Σ_u^—, w ¹Δ_u, and C ³II_u, were investigated in the 1070–1600‐Å region. A 2‐m and a 3‐m vacuum spectrograph, both of normal‐incidence‐type, were used in this work. The observations were extended to high vibration levels for four of the systems, a(v=13), a′(v=15), B′(v=20), w(v=11), while in the C—X system only two bands were analyzed. The progression which was previously ascribed as belonging to the w—X system was studied in detail, and an alternate possibility of this progression being the v″=1 progression of the a—X system was definitely removed. However, a final designation of the upper electronic state must come from a rotational analysis, because the observed T₀₀ of the state differed from that of the w state by approximately 40 cm^—1. The potential energy curves of the low‐lying N₂ states prepared by Mulliken are compared with those calculated by using the presently determined constants.