			15min:

COMPUTATIONAL MOLECULAR SPECTROSCOPY OF FeCO IN THE X ³ Sigma

^- AND 1 ⁵ Sigma

^- ELECTRONIC STATES.

TSUNEO HIRANO, REI OKUDA AND UMPEI NAGASHIMA, Research Institute for Computational Sciences, National Institute of Advanced Industrial Science and Technology, 1-1-1 Umezono, Tsukuba, Ibaraki 305-8568, Japan; PER JENSEN, Theoretische Chemie, Bergische Universität, D-42097 Wuppertal, Germany.

FeCO is a molecule of astrophysical interest. It also served as a bench mark molecule for testing basis sets and ab initio calculation methods.^, We have previously reported molecular constants and relative energies of X ³ Sigma ^- and 1 ⁵ Sigma ^- states of FeCO, based on the two-dimensional ab initio potential energy surfaces (PESs) determined at the MR-SDCI+Q+E_rel/[Roos ANO (Fe, C, O)] and MR-ACPF+E_rel/[Roos ANO (Fe, C, O)] levels of theory. We will report here molecular properties derived from the three-dimensional PESs calculated at the level of MR-SDCI+Q+E_rel/[Roos ANO (Fe, C, O)]. Calculated bond lengths r_e(Fe--C), r_e(C--O), and dipole moment (with experimental r_s bond lengths in parentheses) are 1.722 (1.7270) Å, 1.160 (1.1586) Å, and 3.20 D for the X ³ Sigma ^- state, and 1.844 Å, 1.153 Å, and 0.29 D for the 1 ⁵ Sigma ^- state, respectively. The relative energy of 1 ⁵ Sigma ^- has been calculated to be 1.27 kcal~mol^-1, to be compared with the experimental value of 3.24 kcal~mol^-1. The general trends in low-spin/high-spin issue reported for CoH, CoCN, and NiCN are also observed for the NiCN X ³ Sigma ^- and 1 ⁵ Sigma ^- state pair.