Fourier transform spectroscopy of the low-lying excited electronic states of FeO: A new perturbing Σ state and improved ground state constants

A small rotational perturbation has been found in the 5Δ i ground state of FeO. This occurs in the v = 2 level of the Ω = 2 substate, and only one Λ-boudling component of one rotational level is affected. The perturbing state, which lies about 2100 cm -1 above the lowest spin-orbit level of the molecule, is orbitally nondegenerate, and is likely to belong to the 7Σ + state arising from the configuration (4sσ) 1(3dδ) 2(3dπ) 2(3dσ) 1. The new state, a 7Σ +, is possibly responsible for anomalies in the intensity pattern of the FeO - photodetachment spectrum of Engelking and Lineberger [J. Chem. Phys., 66, 5054-5058 (1977)]. Improved vibrational and rotational constants are presented for the ground state, combining new Fourier transform measurements of the Λ-doubling in X 5Δ 1 with the recent microwave data of Endo et al. [Astrophys. J., 278, L131-132 (1984)]. © 1985.link_to_subscribed_fulltex