Electronic states and nature of bonding in the molecule RhN by all-electron ab initio calculations

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In the present work, all-electron ab initio multi-configuration self-consistent-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 corrections for the one-electron Darwin contact term and the relativistic mass-velocity correction have been determined in perturbation calculations. The spectroscopic constants for the seven low-lying electronic states have been derived by solving the Schrödinger equation for the nuclear motion numerically. The predicted ground state of RhN is 1∑+, and this state is separated from the states 3Π, 1Π, 5Δ, 3∑−, 3Δ and 1Δ by transition energies of 1833, 4278, 6579, 8042, 9632, and 13886 cm−1, respectively. For the 1∑+ ground state, the equilibrium distance has been determined as 1.640 Å, and the vibrational frequency as 846 cm−1. The chemical bond in the 1∑+ electronic ground state has triple bond character due to the formation of delocalized bonding π and σ orbitals. The chemical bond in the RhN molecule is polar with charge transfer from Rh to N giving rise to a dipole moment of 2.08 Debye at 3.1 a.u. in the 1∑+ ground state. An approximate treatment of the spin-orbit coupling effect shows that the lowest-lying spin-orbit coupled state is 0+. This state is essentially derived from the 1∑+ ground state. The second and third state, 0+ and 0−, mainly arise from the 3Π state. The dissociation energy of the RhN molecule in its 1∑+ ground state has been derived as 1.74 eV.