ROTATIONAL, FINE, AND HYPERFINE ANALYSES OF THE (0,0) BAND OF THE D(3)PI-X(3)DELTA SYSTEM OF VANADIUM MONONITRIDE

The VN molecule has been produced in a molecular beam apparatus using a laser vaporization source and its D3PI-X3DELTA (0,0) band has been s tudied by laser-induced fluorescence at low (approximately 0.1 cm-1) a nd sub-Doppler resolution (approximately 0.004 cm-1). Lifetimes of sin gle rotational levels of the D3PI0 component have been measured and in terpreted. Rotational, fine, and hyperfine structures in six of the ni ne subbands possible for a 3PI <-- 3DELTA transition have been recorde d. Both states exhibit a rapid transition from case (a) --> case (b) c oupling cases, manifested by reversals in the Lande patterns of the hy perfine structure. The data have been reduced to a set of 35 molecular constants using a modified case (a(beta)) effective Hamiltonian in wh ich two additional magnetic hyperfine parameters are required for each state. The distortions in the hyperfine structure are due almost enti rely to second-order spin-orbit interaction between states arising fro m the same configuration. Analysis of the derived parameters indicates that the X3DELTA state is well represented by the single electron con figuration ... 8sigma2 3pi4 9sigma1 1delta1, in which the 9sigma molec ular orbital (MO) is a V 4s-4p hybrid (88% V 4s) and the 1delta MO is- a pure V 3d orbital; the dominant configuration for the D3PI state is ... 8sigma2 3pi4 1delta1 4pi1, in which the 4pi MO is an antibonding o rbital composed of at most 82% V 3dpi. The isoconfigurational a 1DELTA and e 1PI states are calculated to lie 3390 and 2200 cm-1 above their respective high spin companions. The lambda doubling in the D3PI0 com ponent has been interpreted in terms of spin-orbit interactions with t he B3SIGMA- and d1SIGMA+ states, both states arising from the ... 8sig ma2 3pi4 1delta2 configuration; the d1SIGMA+ state is known [Simard, M asoni, and Hackett, J. Mol. Spectrosc. 136, 44 (1989)] to lie 102 cm-1 above D3PI0, while the B3SIGMA- state probably lies about 8000 cm-1 b elow.