Knowledge Bank

The reaction of laser-ablated iron atoms with oxygen of nitrous oxide, under supersonic jet-cooled conditions, is a good source of FeO molecules, which are prepared almost entirely in their ground $X5\Delta 4,\nu =0$ State. Laser excitation in the 5500.6300 {\AA} region has given strong laser-induced fluorescence spectra of the orange” system, with sufficient intensity to allow measurement of various bands of the less abundant isotopic molecules ${^{57}}FeO$ and ${^{57}}FeO$. The vibrational structure of the orange” system, recorded $previously1$, has been confirmed, though with the addition of a new weak perturbed bad group at 5660 {\AA}, Which has been rotationally analysed. Deperturbation of the more severely perturbed upper levels had given more accurate isotope shift data, which now suggest that the bands must be assigned to two distinct $\mathrm{<mrow\; data-mjx-texclass="ORD">5</mrow>}\Delta -5\Delta$ electronic transitions, with (0,0) bands at 6110 and 5583 {\AA}. The hyperfine splittings of the low J lines of $\mathrm{<mrow\; data-mjx-texclass="ORD">57</mrow>}FeO$ (2.2% natural abundance) confirm that the electron configuration of the ground state, $\sigma \Delta 3\pi 2$, contains an unpaired electron in a u orbital derived form the Fe 4s atomic orbital: there is no detectable hyperfine splitting in the excited electronic states.