Upper state molecular constants for the (0, 0, 3) and (1, 0, 3) vibration-rotation bands of nitrogen dioxide

High-resolution absorption spectra of the (0,0,3) and (1,0,3) vibration-rotation bands of ¹⁴N ¹⁶O ₂ and ¹⁵N ¹⁶O ₂ were analyzed. Initial values for the ground state constants and predicted values of A, B, and C for the upper states of the (0,0,3) and (1,0,3) bands were taken from previous work. Improved values of the upper state constants including centrifugal distortion and empirical P⁶ terms have been obtained. Further refinement of the ground state constants was not possible. Spin splitting was observed and analyzed for a number of transitions in the (0,0,3) band of both isotopes. Effective spin-rotation coupling constants were obtained for the excited states. Due to the weakness of absorption and lack of resolution no spin splitting was observed in the (1,0,3) bands.