FeO in the X5 A ground state

A rotational spectrum of FeO in its X5 A ground state was described by Endo, Saito and Hirota [253]. Transitions involving relatively low J values were observed for three fine-structure states, with 12 = 4, 3 and 2. Subsequently a much more comprehensive rotational spectrum was measured by Krockertskothen, Knockel and Tiemann [254] using double resonance methods we will discuss these results in the next chapter. More 

The effective Hamiltonian and analysis of the spectra is described in chapter 11 when we discuss the microwave/optical double resonance spectrum. 

For calculation of the matrix elements in case (a) basis, N = J — S note also that x, y stands for the anticommutator xy + yx. 

The spin-rotation constants inequation (10.199) couldnotbe determined, butmost of the other constants were listed. The results indicate that the electron configuration 3e/24v from Ti+(4F) dominates in the ground state of TiCl. At this stage it is difficult to estimate reliably the degree of electron delocalisation, but the structure seems to be mainly ionic. 

It will be clear that pure rotational spectra of more complex orbital and spin states, most of which arise in molecules containing transition metal atoms, are still relatively sparse. This will almost certainly change as experimental techniques develop further a further stimulus is the growing recognition of the importance of these molecules in interstellar and circumstellar space. 

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