Abstract
The infra-red spectra of , HCN, and C give evidence of a splitting of the II vibrational levels (in which a ⊥ vibration is singly excited) into two components which is entirely analogous to the -type doubling of the electronic states of diatomic molecules and is called here -type doubling. The experimental data show that this -type doubling may be represented by and that the constant is of the same order as the constant in . The existence of the -type doubling also explains the apparent discrepancy that the fundamental bands of HCN and do not show a convergence of the and branches while the branch is distinctly shaded to shorter wave-lengths. A preliminary theoretical treatment of the -type doubling is also given. The doubling is due mainly to the fact that in the displaced position of a perpendicular vibration a linear molecule is a slightly asymmetric top, but to some extent also to the Coriolis interaction of different vibrations. The observed values of are all larger than the calculated ones. Taking the -type doubling into account the rotational constants of C have been newly evaluated and from them and the value the rotational constant in the equilibrium position is found to be 0.3906±0.0002 which gives for the moment of inertia g and for the CO distance cm.
DOI:https://doi.org/10.1103/RevModPhys.14.219
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