Rotational, fine, and hyperfine analyses of the (0,0) band of the D 3Π–X 3Δ system of vanadium mononitride

Abstract

The VN molecule has been produced in a molecular beam apparatus using a laser vaporization source and its D 3Π–X 3Δ(0,0) band has been studied by laser-induced fluorescence at low (∼0.1 cm−1) and sub-Doppler resolution (∼0.004 cm−1). Lifetimes of single rotational levels of the D 3Π0 component have been measured and interpreted. Rotational, fine, and hyperfine structures in six of the nine subbands possible for a 3Π ← 3Δ transition have been recorded. Both states exhibit a rapid transition from case (a) → case (b) coupling cases, manifested by reversals in the Landé patterns of the hyperfine structure. The data have been reduced to a set of 35 molecular constants using a modified case (aβ) effective Hamiltonian in which two additional magnetic hyperfine parameters are required for each state. The distortions in the hyperfine structure are due almost entirely to second-order spin–orbit interaction between states arising from the same configuration. Analysis of the derived parameters indicates that the X 3Δ state is well represented by the single electron configuration ...8σ2 3π4 9σ1 1δ1, in which the 9σ molecular orbital (MO) is a V 4s–4p hybrid (88% V 4s) and the 1δ MO is a pure V 3d orbital; the dominant configuration for the D 3Π state is ...8σ2 3π4 1δ1 4π1, in which the 4π MO is an antibonding orbital composed of at most 82% V 3dπ. The isoconfigurational a 1Δ and e 1Π states are calculated to lie 3390 and 2200 cm−1 above their respective high spin companions. The lambda doubling in the D 3Π0 component has been interpreted in terms of spin–orbit interactions with the B 3Σ− and d 1Σ+ states, both states arising from the ...8σ2 3π4 1δ2 configuration; the d 1Σ+ state is known [Simard, Masoni, and Hackett, J. Mol. Spectrosc. 136, 44 (1989)] to lie 102 cm−1 above D 3Π0, while the B 3Σ− state probably lies about 8000 cm−1 below.