Bonds vibrational spectra

Up to now, quantum-mechanical methods have not been applied to the study of the vibrational spectra of cytosine (see Section V, however, for an interpretation of the hydrogen bond vibrational spectra of the quanine-cytosine base pair). 

DYNAMIC PROPERTIES OF H-BONDS AND D-BONDS Vibrational spectra of H-bonds and D-bonds... 

Infrared spectroscopy has been described as one of the most sensitive methods for the detection of hydrogen bonding. Vibrational spectra are significantly altered by hydrogen-bond formation and these changes constitute a criterion for the existence of the bond they provide direct evidence of the role of the proton in the interaction and a measure of the degree of association and strength of the bond. 

The region below 1500 cm"1 is the fingerprint portion of the IR spectrum. A large number of absorptions due to a variety of C-C, C-O, C-N, and C-X single-bond vibrations occur here. 

The V (OCO) ion has a structured electronic photodissociation spectrum, which allows us to measure its vibrational spectrum using vibrationally mediated photodissociation (VMP). This technique requires that the absorption spectrum (or, in our case, the photodissociation spectrum) of vibrationally excited molecules differ from that of vibrationally unexcited molecules. The photodissociation spectrum of V (OCO) has an extended progression in the V OCO stretch, indicating that the ground and excited electronic states have different equilibrium V "—OCO bond lengths. Thus, the OCO antisymmetric stretch frequency Vj should be different in the two states, and the... 

A number of other models were considered and tested (for example, direct B—H bonding). The most significant test was the IR vibrational spectrum, where a sharp absorption band at 1875 cm-1 was found, corresponding to the Si—H stretch mode softened by the proximity of the B-atom. Had the hydrogen been bonded to boron, a sharp absorption band at 2560 cm-1 would have been expected. Also, Johnson (1985) showed that deuteration produced the expected isotopic shift. The most definitive and elegant proof of the correctness of the Si-H-B bonding model was provided by Watkins and coworkers (1990), on the basis of a parametric vibrational interaction between the isotopes D and 10B. 

A complete analysis of the vibrational spectrum had to wait until we were able to prepare T-36 via the photoisomerization of S-2. Even if an anharmonic approximation was taken in account in the calculation (UMP2/6-31G ) the IR spectrum was still in poor agreement with the observed spectrum.64 But one thing was clear formula T-36 does not represent the real structure of propargylene, since no IR band in the expected region for the C,C triple bond vibration of an acetylene was found, but a C,C stretching vibration at 1620 cm-1 was registered instead. 

The imaginary part of %a(co) proportional to the absorption spectrum for impurity bond vibrations is specified by the relation ... 

The vibrational spectrum of methylguanine-methylcytosine (GC) complex consists of 99 normal modes frequencies. Differently from the AT base pair, in the GC complex the normal modes of the two bases are coupled together, thus an analysis of the shift relatively to the isolated bases is extremely complicated. This stronger coupling can possibly he ascribed to the presence of three h-bonds, rather than two as in AT. However, we tentatively discuss some significant shifts. 

Because IR absorption is caused by bond vibrations, and all solvents are molecules that, by definition, have atoms bonded to one another, all compounds have absorption features in the MIR region of the spectrum. Thus, most... 

M. E. Senent, A. Nino, C. Munoz Caro, Y. G. Smeyers, R. Dominguez Gomez, and J. M. Orza, Theoretical study of the effect of hydrogen bonding on the stability and vibrational spectrum of isolated 2,2,2 trifluoroethanol and its molecular complexes. J. Phys. Chem. A 106, 10673 10680 (2002). 

An infrared spectrum can be obtained for a sample of an organic compound regardless of its physical state (solid, liquid, gas or dissolved in a solvent). Infrared radiation is passed through the sample in the spectrometer. Some wavelengths are absorbed, causing bond vibrations within the molecules. The transmitted radiation then passes to a detector where the intensity at different wavelengths is measured. An Infrared spectrum, like that shown in the diagram, is obtained. 

---