Carbon monoxide vibrational analysis

Korzeniewski C, Pons S, Schmidt PP, Severson MW. 1986. A theoretical analysis of the vibrational spectrum of carbon monoxide on platinum metal electrodes. J Chem Phys 85 4153-4160. 

Carbonylchlorocopper(I) is a colorless crystalline substance that decomposes rapidly in the absence of a carbon monoxide atmosphere to give copper(I) chloride and carbon monoxide. The compound is, however, stable for long periods of time if stored under carbon monoxide. Cu(CO)Cl has a polymeric structure,10 which may be described as layers of fused, six-membered, copper-chloride rings in the chair conformation, with terminally bonded carbonyl ligands. The infrared spectrum of Cu(CO)Cl (Nujol mull at 0°C) displays a characteristic large peak at 2127 cm -1 and a vibrational analysis has been reported.13... 

Fia. VII-4.—Some observed energy levels for the carbon monoxide molecule, as determined by the analysis of spectra. The first thirteen vibrational levels are shown for the normal electronic state of the molecule, and the rotational levels are Bhown for the lowest vibrational state. 

The selection rule for a diatomic molecule is that the vibrational quantum number changes by 1, at least under the harmonic approximation of the potential. Also, the dipole moment has to change in the course of the vibration or else the transition is forbidden. Carbon monoxide, for instance, has an allowed fundamental transition, whereas N2 does not. The separation of variables that is accomplished with the normal mode analysis says that each mode can be regarded as an independent one-dimensional oscillator. Thus, we can borrow the results for the simple harmonic oscillator to conclude that a transition will be allowed if the vibrational quantum number for any single mode changes by 1 where the vibrational motion in that mode corresponds to a changing dipole moment. 

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