Carbon dioxide structure, vibrational

Two important applications of radiation to determine molecular structure—X-ray crystallography and magnetic resonance—were discussed in Chapters 3 and 5. In this chapter we will discuss a variety of other techniques. Microwave absorption usually forces molecules to rotate more rapidly, and the frequencies of these absorptions provide a direct measure of bond distances. Individual bonds in a molecule can vibrate, as discussed classically in Chapter 3. Here we will do the quantum description, which explains why the greenhouse effect, which overheats the atmosphere of Venus and may be starting to affect the Earth s climate, is a direct result of infrared radiation inducing vibrations in molecules such as carbon dioxide. 

There is now a growing literature of nickel organometallic complexes that contain carbon dioxide or related cumulene ligands that result from reactions with carbon monoxide. The first structurally characterized complex of carbon dioxide was the nickel complex Ni(G02)(PCy3)2 reported in 1975. A more recent study of this complex provides the complete assignments of the vibrational spectra and theoretical calculations of different isomers in support of a mechanism for CO2 fluxionality that involves end-on coordination. The tridentate pincer ligand 2,6-bis((diiso-propylphosphino)methyl)phenyl (PGP) has been used to form the square-planar Ni(ii) hydroxide complex Ni(OH)(PGP). The complex Ni(OH)(PCP) reacts with CO to give a binuclear /X-GO2 complex (Equation (2)). 

The Raman spectrum of quenched products (Fig. 7) consists of the symmetric stretching of excess P-O2 at 1585 cm, two Fermi-resonance bands of CO2 at 1270 and 1400 cm", and three new additional sharp bands at 734, 1079, and 2242 cm". The systematic of the latter three bands are very similar to those of nitrosonium nitrate N0" N03", an ionic dimer of nitrogen dioxide. This similarity suggests that the products also include a species with carbonates and carbosonium, CO COa ". The vibrations of carbonate ions appear at 713 and 1082 cm" in CaCOs [84], and the CO vibration appears about 2150 cm" at 5 GPa [85]. Electronic structure calculations for [86, 87] suggest that there are several low lying states of CO " ", whose vibrational frequencies vary between 1000 and 2000 cm". The yield of... 

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