15min:

SACHIKO S. ITONO AND TSUNEO HIRANO, Department of Chemistry, Faculty of Science, Ochanomizu University, Tokyo 112-8610, Japan; UMPEI NAGASHIMA, Tsukuba Advanced Computing Center, National Institute of Advanced Industrial Science and Technology, Ibaraki 305-8562, Japan.

To answer the long-standing debate which state is the electronic ground state of FeN, highly correlated ab initio molecular orbital calculations with or without relativistic corrections and spin-orbit coupling interaction have been carried out for several low-lying electronic states including the ² , ⁴ , ⁴ , ² , ² , and ^{6 +} states. The MR-ACPF calculations as well as the MR-SDCI + Q calculations showed that the electronic ground state of FeN is ² . Coinsidence between the predicted spectroscopic constants and those observed by Aiuchi et al. and Ziurys et al. shows that the state they observed is the X² ~ =2/5 spin substate. The equilibrium bond length r_e, rotational constant B₀, centrifugal distortion constant D_J, harmonic frequency _e, anharmonicity constant _ex_e , and spin-orbit coupling constant A predicted for the X² state at the MR-ACPF level are 1.5752 Å, 0.60334 cm^-1, 1.17 x 10^-6 cm^-1, 890 cm^-1, 8.2 cm^-1, and -362 cm^-1, respectively.