CO stretching modes

Vibrational spectroscopy has generally been applied to Si—M complexes in order to assign Si—M, M—Cl, M—P, or M—CO stretching mode(s). 

The lower frequency, axial CO stretching mode, peak is well separated in the manganese and rhenium compounds. As suggested by Fig. 8 this is a situation in which intermediate mode behaviour may be expected. Figure 10 shows that this is... 

Jung, C., et al. (1992) Substrate analouge induced changes of the CO-stretching mode in cytochrome P450cam -carbon monoxide complex. Biochemistry 31, 12,855-12,862. 

Resonances with pure excitation of the CO stretching mode (0, U2, 0) (an example with Vi - 8 is shown in Fig. 5) have the smallest rate and therefore the longest lifetime energy transfer from r to R is rather inefficient, and therefore the system needs a long time before enough eneigy is accumulated in the dissociation coordinate to permit dissociation. On the other extreme, direct excitation in R allows a rather rapid bond rupture, and therefore the resonances (t>i, 0, 0) have the shortest lifetimes. Excitation of the bending mode (0,0, U3) leads to lifetimes that are between C-O excitation as the lower limit and H-C excitation as the upper extreme. This mode specificity is further elucidated in Fig. 8, where we show the widths for several... 

Two results appear immediately from the study of CO on Mo2C. First, the TPD data show that CO only partially dissociates on Mo2C. Dissociation on Mo2C leads to high temperature recombinative desorption of CO. However, the ratio of the area of the latter peak to the saturation area of the 325 K feature is 0.2. Second, the RAIRS spectra display a single v(CO) stretching mode with a frequency characteristic of on-top bonded... 

In C-coordinated complexes, the frequency splitting between the two v(CO) stretching modes is less than 400 cm-1, and in end-on complexes, the out-of-plane bending mode y(C=0), located in the 500-650cm-1 region, exhibits a preponderant lsO effect, in contrast with other coordination modes, where a larger 13C effect is observed (namely Ay(13C) = 10 to 20cm-1, versus Ay(180) = 5 cm-1). 

The calculated harmonic vibrational frequencies can be compared with two experimental IR bands at 1867 and 953 cm"1. The three computed frequencies are similar and indicate that the two experimental bands can be associated to the TiO and especially the CO stretching modes of the A excited state. 

The experimental MC and CO bond lengths are well reproduced by the calculations. For the CO stretching mode, the ratio of the experimental anharmonic (2143 cm-1) to the harmonic frequency (2170 cm-1) is equal to 0.988. The calculated harmonic vcoreproduces well the harmonic CO frequency. The vco 2x11 / Vco Cal° ratios obtained fit this value with an accuracy equal to or better than 1%, showing that the method used for the frequency calculation is accurate enough. Hence, the chosen method appears to be adequate for our study,... 

In the previous examples for molecules with relatively few atoms, we studied and presented the results of all 31V-6 vibrations of the molecules. However, for molecules composed of a large number of atoms, often it is convenient to concentrate on a certain type of vibration. The prime example of this kind of investigation is the enumeration of the CO stretching modes in metal carbonyl complexes. 

So there are two and three CO stretch bands in the infrared and Raman spectra, respectively. The CO stretching modes and their frequencies are given in Fig. 7.3.11. 

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