Ab Initio Multireference Singles and Doubles Configuration Interaction Study of the Low-Energy States of Iron Mononitride

Low-lying states of iron mononitride are studied using ab initio multireference singles and doubles configuration interaction (MR-SDCI) calculations. For each one of the (2)Delta, (4)Pi, (6)Sigma(+), (2)Pi, (4)Delta, (6)Delta P, and (6)Delta states the reference wavefunction has been obtained at the complete active space self consistent field (CASSCF) level and relativistic corrections were included. Potential energy curves are presented for all states. Spectroscopic constants have been determined for the (2)Delta, 4 Pi, and 6 Sigma(+) states assuming a Morse-type potential function using a code written by one of us. For the (2)Delta state, the calculated spectroscopic constants are R(e) 1.567 angstrom, omega(e) = 827 cm(-1), and mu = 1.68 D. Rotovibrational analysis suggests that the third vibrational level of the (2)Delta state already surpasses the first vibrational levels of the (4)Pi and (6)Sigma(+) states, what reassures the difficulty in correctly attributing the lines of the experimental spectrum. (C) 2010 Wiley Periodicals, Inc. Int J Quantum Chem 111: 1453-1457, 2011