ABSORPTION SPECTRUM OF THE NO MOLECULE: IV. THE G2Σ−–X2Π SYSTEM

Abstract

High-dispersion plates of the NO absorption spectrum have been studied between 1600 and 1390 Å for the three isotopic molecules N¹⁴O¹⁶, N¹⁵O¹⁶, and N¹⁴O¹⁸, and G²Σ⁻–X²Π bands were sorted out from the many overlapping bands in the spectrum. The well-defined band system satisfies the established isotope relations. In contrast with most of the other known NO band systems G²Σ⁻–X²Π shows almost no perturbations. Vibrational and rotational analyses gave the following constants for the G²Σ⁻ state of N¹⁴O¹⁶: T_e = 62911.7 cm⁻¹; ω_e = 1085.54 cm⁻¹, ω_ex_e = 11.083 cm⁻¹, ω_ey_e = −0.1439 cm⁻¹, B_e = 1.2523 cm⁻¹, α_e = 0.0204 cm⁻¹, γ_e = 1.3426 Å. The combination defect observed in the G²Σ⁻–X²Π bands agrees with the defect found in the A²Σ⁺–X²Π(γ) bands except in sign, which is opposite. Therefore, the symmetry of the G state is confirmed as ²Σ⁻. The "pure precession" relation between G²Σ⁻ and X²Π is found to hold for the Λ-type doubling of X²Π. The diffuse structure of the band assigned to ν = 10 indicates that G²Σ⁻ is predissociated by a repulsive ²Σ⁻ state dissociating into ²D(N)+³P(O) atoms at 71660 cm⁻¹. The dissociation energy and electron configuration for G²Σ⁻ are discussed.