Absorption spectroscopy calculation specifics

Fairly good agreement exists between the calculated value of 1682 cm-1 and the experimental value of 1650 cm-1. Based upon the Hooke s law approximation, numerous correlation tables have been generated that allow one to estimate the characteristic absorption frequency of a specific functionality [3], It becomes readily apparent how IR spectroscopy can be used to identify a molecular entity, and subsequently to physically characterize a sample or to perform quantitative analysis. 

The last paper <91G477> deals more specifically with the problem of tautomerism of 3(5)-phenyl-pyrazole (57). By the use of UV spectroscopy, semiempirical calculations (CNDO/S//CNDO/2) and low temperature C NMR spectroscopy the tautomeric equilibrium (80% (57a), 20% (57b) was determined. One of the most important conclusions of this work, as far as electronic spectra are concerned, is that the absorption of phenylpyrazoles is much more dependent on the conformation of the phenyl ring than on its position, 3, 4, or 5. 

The characterization of the unoccupied and partially occupied states of TTF-TCNQ has recently been the object of a combined X-ray absorption near edge spectroscopy (XANES) and SIESTA study [234]. The use of synchrotron radiation allowed the determination of the partial DOS of S, N, and C because of the element selectivity of X-ray absorption and the determination of the spatial distribution of the molecular orbitals due to the polarization of the synchrotron hght. The SIESTA computations were used to calculate the DOS and PDOS into the carbon, nitrogen, and sulfur of TTF, TCNQ, and TTF-TCNQ. As a consequence, an in-depth discussion of the origin of the different features of the unoccupied DOS of the three materials, TTF, TCNQ, and TTF-TCNQ, has been possible leading to the assignment of most of the experimentally obtained features to specific molecular orbitals. 

The energies calculated from equation 6.1 for the infrared and Raman frequencies lie in the range of the vibrational and rotational motions of molecules. Infrared and Raman spectroscopy provide structural information once the various absorption bands are assigned to specific molecular vibrations. Similarly, the energies associated with the visible and ultraviolet radiation lie in the range of electronic transitions within the atoms and provide information about chemical bonding. Electromagnetic radiation is the most widely used because of the availability of sources and detectors and the interpretation of the data in... 

---