Spectra Compilations

P-nmr, and a large coUection of C-nmr spectra compiled by Bremser at BASE (68,69). It also offers B-nmr spectra compiled by Nitth at the University of Munich. 

Two pattern recognition techniques are applied to the analysis of the library of FTIR spectra compiled by the US EFA> The patterns which emerge demonstrate the influence of molecular structure on the spectra in a way familiar to chemical spectroscopists They are also useful in evaluation of the library, which is not error free, and in assessing the difficulties to be expected when using FTIR spectra for complex mixture analysis. 

A PC-based 1H-nmr database, which includes full spectrum search capability, is being constructed by the Toyohashi University of Technology (67). Speclnfo, owned by Chemical Concepts, offers a 150,000 spectra library and database system for mainframe computers, which includes H, 15n, 19f, 17o, 31P-nmr, and a large collection of 13C-nmr spectra compiled by Bremser at BASF (68,69). It also offers nB-nmr spectra compiled by Nu th at the University of Munich. 

Moreover, TR-XAFS data reduction needs to be performed even at an early stage of a TR-XAFS experiment. To use the available beamtime as efficiently as possible, it is crucial to monitor the progress of a TR experiment by a continuous analysis of the measured spectra. (Compilations of XAFS software can be found at http //www.esrf.fr/computing/... 

The principles and applications of UPS have been described in the monographs by Turner and coworkers1, Eland2 and Rabalais3, and in the extensive series edited by Brundle and Baker4. Of particular use to the experimentalist is the handbook of spectra compiled by Kimura and coworkers5. 

Another disadvantage is that all the spectra compiled are not recorded under standard conditions. The spectra come from many sources and types of analyzers and were recorded on devices whose calibrations are uncertain (is the ionization energy always precisely at 70 eV ). The purities and concentrations of reference molecules are variable. In conclusion, if you use a marketed database, consider the results cautiously. 

Figure 4.3-1 Rotation-vibration spectrum of A infrared spectrum in absorbance units for the experimental conditions, see also Fig. 4.3.1-9. B Raman spectrum, compiled from several spectra recorded under different conditions, but plotted on an approximately equivalent intensity scale. The peaks of r l and vj are off scale (pressure 13 kPa, laser power 6 to 10 W at 514.5 nm, spectral slitwidth about 2 cm ).

Figure 2 Molybdenum K-edge X-ray absorption spectrum, ln(i /i ) versus X-ray energy (eV), for molybdenum metal foil (25- jjn thick), obtained by transmission at 77 K with synchrotron radiation. The energy-dependent constructive and destructive interference of outgoing and backscattered photoelectrons at molybdenum produces the EXAFS peaks and valleys, respectively. The preedge and edge structures marked here are known together as X-ray absorption near edge structure, XANES and EXAFS are provided in a new compilation of literature entitled X-rsy Absorption Fine Structure (S.S. Hasain, ed.) Ellis Norwood, New York, 1991.

State-of-the-art for data evaluation of complex depth profile is the use of factor analysis. The acquired data can be compiled in a two-dimensional data matrix in a manner that the n intensity values N(E) or, in the derivative mode dN( )/d , respectively, of a spectrum recorded in the ith of a total of m sputter cycles are written in the ith column of the data matrix D. For the purpose of factor analysis, it now becomes necessary that the (n X m)-dimensional data matrix D can be expressed as a product of two matrices, i. e. the (n x k)-dimensional spectrum matrix R and the (k x m)-dimensional concentration matrix C, in which R in k columns contains the spectra of k components, and C in k rows contains the concentrations of the respective m sputter cycles, i. e. ... 

Fluorine spectra of two fluoroethylenes, both from the Japan Halon compilation [19], are shown m Figures 4 and 5. The splitting pattern of fluoroethene (doublet of doublets of doublets) is clarified by using a branching display above the peaks, from which coupling constants can be measured easily. The AA XX spectrum of 1,1-difluoroethene is also shown. 

Computer Techniques McLafferty (Ref 63) has pointed out that the usefulness of elemental composition information increases exponentially with increasing mass, since the number of elemental combinations with the same integral mass becomes larger. There are compilations of exact masses and elemental compositions available (Refs 12a, 13 18a). Spectral interpretation will be simplified in important ways if elemental compositions of all but, the smallest peaks are determined. Deriving the elemental compositions of several peaks in a spectrum is extremely laborious and time-consuming. However, with the availability of digital computers such tasks are readily performed. A modern data acquisition and reduction system with a dedicated online computer can determine peak centroids and areas for all peaks, locate reference peaks, interpolate between them to determine the exact masses of the unknown peaks, and find within minutes elemental compositions of all ions in a spectrum (Refs 28b 28c)... 

Room-temperature fluorescence (RTF) has been used to determine the emission characteristics of a wide variety of materials relative to the wavelengths of several Fraunhofer lines. Fraunhofer lines are bands of reduced intensity in the solar spectrum caused by the selective absorption of light by gaseous elements in the solar atmosphere. RTF studies have recently included the search for the causes of the luminescence of materials and a compilation of information that will lead to "luminescence signatures" for these materials. For this purpose, excitation-emission matrix (EEM) data are now being collected. 

A review of the early experimental works can be found in references [56-58]. More recently, Chutjian recorded the electron-impact excitation spectrum of formaldehyde [59,60] and reported transition energies that are taken as reference values in many other works. So are the experimental values compiled by Robin [61]. 

Figures 6 and 7. Spectra were run on a Perkin-Elmer Model 467 grating spectrophotometer as a KC1 pellet (1 mg/200 mg KCl), and as a Nujol mull (20 mg/3 drops). The spectra are essentially identical. The CTC-HC1 spectrum may also be found in a compilation of IR spectra of Drug Reference Standards by Hayden et al. (26). Major absorption frequencies have been compiled (27) and assignments have been made on many of the bands(28-31). Some of the major frequencies and band assignments are ...

Sodium valproate was not sufficiently volatile for mass spectral analysis. The mass spectrum of valproic acid as shown in Figure 5 was obtained using an Associated Electrical Industries Model MS-902 Mass Spectrometer with the ionization electron beam energy at 70 eV. High resolution data were compiled and tabulated with the aid of an on-line PDP-11 Computer. 

Phosphorescence data of several nitronaphthalenes, mainly from the recent literature 2-6 68-70) have been compiled in Table 1. A thorough analysis of the absorption spectrum of 1-nitronaphthalene has also appeared... 

To provide the necessary data on NO, the entire SFR laser - OA absorption system was enclosed in a capsule and flown to an altitude of 28 kM for real time in situ measurements." Figures 7(a) and (b) show the OA spectrum of ambient air (at 28 kM) analyzed before sunrise and at local noon. The lack of NO before sunrise and large concentration of NO at room is clearly seen. Figure 8 shows a summary of all the data compiled on two such balloon flights. We see that the measurements provide 1) absolute concentration of NO and 2) its diurnal variation. Many of the details of the model proposed above are confirmed (see Ref. 11 for details). 

The data base that is used in the CNMR search system consists currently of 4,100 CNMR spectra (3). As in the case of the MSSS, every compound has a CAS registry number, and all exact duplicate spectra have been removed from the file. A specific compound may still appear in this file more than once, however, because its CNMR spectrum may have been recorded in different solvents. The CNMR file is still small but is growing at a fairly steady rate and should benefit considerably from recent international agreements to the effect that all major compilations of CNMR data will, in the future, be pooled. 

Classical natural products chemistry involved the isolation and purification of major natural product compounds from specific representatives of flora or fauna for structure determination. The terpenoids are the compounds of interest in this chapter and their initial structure elucidations were carried out in the 1930s—1970s. There are numerous compilations and encyclopaedia on terpenoids listing the physicochemical properties and literature background of the pure natural products. Many of the mass spectra of the underivatized terpenoid compounds are in the standard mass spectrum libraries of modern computerized data systems. 

For this task, easily accessible properties of mixtures or pure metabolites are compared with literature data. This may be the biological activity spectrum against a variety of test organisms. Widely used also is the comparison of UV [90] or MS data and HPLC retention times with appropriate reference data collections, a method which needs only minimal amounts and affords reliable results. Finally, there are databases where substructures, NMR or UV data and a variety of other molecular descriptors can be searched using computers [91]. The most comprehensive data collection of natural compounds is the Dictionary of Natural Products (DNP) [92], which compiles metabolites from all natural sources, also from plants. More appropriate for dereplication of microbial products, however, is our own data collection (AntiBase [93]) that allows rapid identification using combined structural features and spectroscopic data, tools that are not available in the DNP. 

Erowid.org is an online library of information about psychoactive plants and chemicals and related topics. The information on the site is a compilation of the experiences, words, and efforts of hundreds of individuals including users, parents, health professionals, doctors, therapists, chemists, researchers, teachers, and lawyers. Erowid acts as a publisher of new information as well as a library for the collection of documents published elsewhere. The information found on the site spans the spectrum from solid peer reviewed research to fanciful creative writing. 

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