High-resolution Fourier spectrometry of 14N2 and 15N2 infrared emission spectrum: Extensive analysis of the W3Δu - B3Πg system

The infrared spectrum of the nitrogen molecule, excited in a microwave discharge, has been recorded in high resolution by Fourier spectrometry in the range 2500–15 000 cm^?1. The precision of the measurements is estimated to be about 0.003 cm^?1. We have analyzed 19 bands of the W³Δ_u-B³Π_g system of ¹⁴N₂, with 0 ≤ v′ ≤ 7, and three bands of ¹⁵N₂ lying between 2500 and 5900 cm^?1. The molecular constants of the ³Δ_u and B³Π_g states have been determined by direct approach using an iterative nonlinear least-squares procedure. It has proved convenient to describe the levels of W³Δ_u state in a case a basis although in fact they approximate those of Hund's case b. Derived values of equilibrium constants of W³Δ_u are, in cm^?1: T_e = 8875.3347 (with origin taken in A, ³Σ_u⁺v = 0 level); ω_e = 1506.4859; ω_eχ_e = 12.5469; B_e = 1.4702537; α_B = 0.0170389; D_e = 0.55958 × 10^?5. RKR potential energy curves for the two states are constructed, and the Franck-Condon factors calculated for the W-B system.