ELECTRONIC STATES AND NATURE OF BONDING IN THE MOLECULE RHN BY ALL-ELECTRON AB-INITIO CALCULATIONS

In the present work, all-electron ab initio multi-configuration self-c onsistent-field (CASSCF) and multi-reference configuration interaction (MRCI) calculations have been carried out to determine the low-lying electronic states of the molecule RhN. In addition, the relativistic c orrections for the one-electron Darwin contact term and the relativist ic mass-velocity correction have been determined in perturbation calcu lations. The spectroscopic constants for the seven low-lying electroni c states have been derived by solving the Schrodinger equation for the nuclear motion numerically. The predicted ground state of RhN is (1) Sigma(+), and this state is separated from the states (II)-I-3, (II)-I -1, (5) Delta, (3) Sigma(-), (3) Delta and (1) Delta by transition ene rgies of 1833, 4278, 6579, 8042, 9632, and 13886 cm(-1), respectively. For the (1) Sigma(+) ground state, the equilibrium distance has been determined as 1.640 (A) over circle, and the vibrational frequency as 846 cm(-1). The chemical bond in the (1) Sigma(+) electronic ground st ate has triple bond character due to the formation of delocalized bond ing pi and sigma orbitals. The chemical bond in the RhN molecule is po lar with charge transfer from Rh to N giving rise to a dipole moment o f 2.08 Debye at 3.1 a.u. in the (1) Sigma(+) ground state. An approxim ate treatment of the spin-orbit coupling effect shows that the lowest- lying spin-orbit coupled state is 0(+). This state is essentially deri ved from the (1) Sigma(+) ground state. The second and third state, 0( +) and 0(-), mainly arise from the (II)-I-3 state. The dissociation en ergy of the RhN molecule in its (1) Sigma(+) ground state has been der ived as 1.74 eV. (C) 1997 Elsevier Science B.V.