Infrared data, experimental

More recently, infrared data have found further application in conformational studies of complex quinolizine derivatives, such as the previously mentioned alkaloid cytisine 9. Comparison of experimental values for the and t co) frequencies with the theoretical values obtained from semi-empirical calculations for... 

Infrared spectra of PAHs and PACs are also available, in part because of interest in PAHs in interstellar space (e.g., see Hudgins and Sandford, 1998a, 1998b, 1998c and Langhoff et al., 1998). Their theoretical treatment and experimental infrared data may also prove useful in studies related to the troposphere. 

In association with infrared data, Raman spectra are invaluable in assigning CO-stretching frequencies. Few Raman data for carbonyl compounds are available, however, because of the experimental difficulties involved. Solutions of the compounds at high concentrations are required to obtain acceptable Raman data unfortunately, many carbonyl compounds are insufficiently soluble in the appropriate solvents. There are a few examples, however, where this problem of solubility has been circumvented by employing another phase. Thus, Raman data have been reported for the compounds, M(CO)5 (M = Mo, Cr, or W) (8), M2(CO)io [M = Re (104, 122, 179, 220) or Mn (122)] -, Mn(CO)sBr (122), Re(CO)6l (179), and Re3(CO)i2H3 (277) in the solid state and Ni(CO)4 in the gas phase (39). Another limitation is that decomposition or isomerism of the compound may occur on irradiation. The fact that all colored compounds absorb the mercury excitation line at 4358 A poses an additional problem. However, it is possible to use the helium lines at 5876, 6678, and 7065 A to obtain Raman spectra, as has been done for the compounds Fe(CO)s (283), HFe(CO)4-, Fe(CO) -, Co(CO)4- (282), M[Co(CO)4]2 (M = Cd or Hg) (281), and Ni(CO)4 (280). Further, the use of laser sources in the measurement of Raman spectra overcomes many of these difficulties this technique is now being applied extensively (122, 179, 198). 

C-M-C-bending vibrations result in absorption spectra in the region of 100 cm . Three general methods exist for obtaining the frequencies corresponding to these modes direct measurement of (i) the infrared and (ii) the Raman spectra in this region and (in) the use of relevant combination band data. Experimental difficulties are experienced in... 

Only v3 is directly observed in the infrared. All of the frequencies for NpF6 lie intermediate between UF6 and PuFa. The infrared data make it possible to deduce the value of the Raman active frequencies in the case of uranium hexafluoride, a discrepancy was revealed between the value for the Raman spectrum as deduced by the method of Gaunt (88) from infrared measurements and the experimentally determined Raman spectrum of Bigeleisen et al. (10). Consequently, Claassen et al. (17) have measured... 

The difference between the absorbed solar radiation and the net infrared radiation. Experimental data show that radiation from the earth s natural surfaces is rather close to the radiation from a black body at the corresponding temperature the ratio of the observed values of radiation to black body radiation is generally 0.90 -1.0. radiative-convective models... 

The spectrum of a low temperature Xe + HCl mixture in the 40-80 cm region is shown in Fig. 4. Structure due to the Xe-HCl complex is very extensive, and considerably stronger than that of Ar-HCl. Again, much of this structure has been observed previously by Boom and van der Elsken at low resolution. The molecular beam electric resonance spectrum of Xe-HCl has been studied by Chance et al., but there are no reported high resolution mid- or far-infrared spectra of this complex (though Howard and Pine have some unpublished mid-infrared data). The numerous isotopes of xenon and its relatively high cost may help to explain the scarcity of experimental results. 

In order to derive structural information from infrared frequencies, input is required from quantum chemical calculations at computational levels which match the experimental resolution. Experimentally, gas-phase conditions imply extremely low sample densities, requiring special techniques in order to acquire infrared data. Some of those techniques involve double resonance approaches which provide unique opportunities for isomer selective IR spectroscopy. This facet is among the advantages of gas-phase experiments, making it possible to follow certain properties, such as excited state dynamics, as a function of molecular structure. At the same time, the availability of gas-phase data provides opportunities to calibrate computational methods, force fields, and functionals. 

Artificial Intelligence in Chemistry Chemical Engineering Expert Systems Chemometrics Multivariate View on Chemical Problems Electrostatic Potentials Chemical Applications Environmental Chemistry QSAR Experimental Data Evaluation and Quality Control Fuzzy Methods in Chemistry Infrared Data Correlations with Chemical Structure Infrared Spectra Interpretation by the Characteristic Frequency Approach Machine Learning Techniques in Chemistry NMR Data Correlation with Chemical Structure Protein Modeling Protein Structure Prediction in ID, 2D, and 3D Quality Control, Data Analysis Quantitative Structure-Activity Relationships in Drug Design Quantitative Structure-Property Relationships (QSPR) Shape Analysis Spectroscopic Databases Structure Determination by Computer-based Spectrum Interpretation. 

The experimental data and arguments by Trassatti [25] show that at the PZC, the water dipole contribution to the potential drop across the interface is relatively small, varying from about 0 V for An to about 0.2 V for In and Cd. For transition metals, values as high as 0.4 V are suggested. The basic idea of water clusters on the electrode surface dissociating as the electric field is increased has also been supported by in situ Fourier transfomr infrared (FTIR) studies [26], and this model also underlies more recent statistical mechanical studies [27]. 

Specinfo, from Chemical Concepts, is a factual database information system for spectroscopic data with more than 660000 digital spectra of 150000 associated structures [24], The database covers nuclear magnetic resonance spectra ( H-, C-, N-, O-, F-, P-NMR), infrared spectra (IR), and mass spectra (MS). In addition, experimental conditions (instrument, solvent, temperature), coupling constants, relaxation time, and bibliographic data are included. The data is cross-linked to CAS Registry, Beilstein, and NUMERIGUIDE. 

A predictive macromolecular network decomposition model for coal conversion based on results of analytical measurements has been developed called the functional group, depolymerization, vaporization, cross-linking (EG-DVC) model (77). Data are obtained on weight loss on heating (thermogravimetry) and analysis of the evolved species by Eourier transform infrared spectrometry. Separate experimental data on solvent sweUing, solvent extraction, and Gieseler plastometry are also used in the model. 

---