Computational spectrometry

Dunham s Formalism Applied in Reduction of Spectral Data of Diatomic Molecules and the Development of Computational Spectrometry... 

We examine the derivation of information about molecular structure and properties from analysis of pure rotational and vibration-rotational spectral data of diatomic molecular species on the basis of Dunham s algebraic formalism, making comparison with results from alternative approaches. According to an implementation of computational spectrometry, wave-mechanical calculations of molecular electronic structure and properties have already played an important role in spectral reduction through interaction of quantum chemistry and spectral analysis. 

Computational spectrometry, which implies an interaction between quantum chemistry and analysis of molecular spectra to derive accurate information about molecular properties, is needed for the analysis of the pure rotational and vibration-rotational spectra of HeH in four isotopic variants to obtain precise values of equilibrium intemuclear distance and force coefficient. For this purpose, we have calculated the electronic energy, rotational and vibrational g factors, the electric dipolar moment, and adiabatic corrections for both He and H atomic centres for intemuclear distances over a large range 10 °m [0.3, 10]. Based on these results we have generated radial functions for atomic contributions for g g,... 

As an application of this implementation of computational spectrometry, we present preliminary results of analysis of frequencies of pure rotational and vibration-rotational transitions, from the literature, of FIeFI in four isotopic variants formed from Fle, Fle, FI and in appropriate combinations. With the values of and in Table 4, we evaluated the auxiliary... 

Most of the previous discussion has concerned addition. Subtraction in binary is very similar, but multiplication is awkward (try it ). For this reason it is quicker for a computer to multiply by carrying out a series of additions. Multiplying 3x5 becomes adding 5 -(- 5 -(- 5. Because each addition is very fast, the time taken for even a large multiplication is very little and still appears instantaneous to us. Only with very large computations does this speed become obvious enough to merit special computers, more powerful than the ones being considered here for use in mass spectrometry. Finally, division is very similar to multiplication, except that a series of subtractions is carried out instead of additions. 

Chapman, J.R., Computers in Mass Spectrometry, Academic Press, London, 1978. 

McMaster, M.C. and McMaister, C., GC/MS A Practical User s Guide, Wiley, Chichester, U.K., 1998. Meisel, W.S., Computer Orientated Approaches to Pattern Recognition, Academic Press, New York, 1972. Mellon, F.A., Selh, R., and Startin, J.R., Mass Spectrometry of Natural Substances, Royal Society of Chemistry, London, 2000. 

Energy Spectrometry (EDS) uses the photoelectric absorption of the X ray in a semiconductor crystal (silicon or germanium), with proportional conversion of the X-ray energy into charge through inelastic scattering of the photoelectron. The quantity of charge is measured by a sophisticated electronic circuit linked with a computer-based multichannel analyzer to collect the data. The EDS instrument is... 

If you frequently analyze pesticides, obtain the latest edition of Mass Spectrometry of Pesticides and Pollutants (Safe and Hutzinger. Boca Raton, FL, CRC Press). This book, combined with the list of most abundant ions (Table 25.1) and/or a computer library search, will be sufficient to identify most commercial pesticides. Also, see Chapters 17, 26, and 27. 

Micromass, the mass spectrometry company, for permission to use their technical literature and application notes and, in particular, Chris Herbert for helpful discussions and access to his computer graphics. 

The mass spectrometry employed electrospray ionization and each metabolite gave an [M + H]+ ion which was then used as a precursor ion for a product-ion MS-MS scan. For subsequent MS" experiments, the base peak of the previous MS-MS experiment was chosen under computer control and this allowed all analytes to be studied in a single chromatographic separation. 

The following is a procedure recommended for elucidating the structure of complex organic molecules. It uses a combination of different NMR and other spectroscopic techniques. It assumes that the molecular formula has been deduced from elemental analysis or high-resolution mass spectrometry. Computer-based automated or interactive versions of similar approaches have also been devised for structural elucidation of complex natural products, such as SESAMI (systematic elucidation of structures by using artificial machine intelligence), but there is no substitute for the hard work, experience, and intuition of the chemist. 

Barkley J, Bunch J, Bursey JT, et al. 1980. Gas chromatography mass spectrometry computer analysis of volatile halogenated hydrocarbons in man and his environment. A multimedia environmental study. Biomed Mass Spectrom 7 139-147. 

Thermal desorption spectroscopy and temperature programmed reaction experiments have provided significant insight into the chemistry of a wide variety of reactions on well characterized surfaces. In such experiments, characterized, adsorbate covered, surfaces are heated at rates of 10-100 K/sec and molecular species which desorb are monitored by mass spectrometry. Typically, several masses are monitored in each experiment by computer multiplexing techniques. Often, in such experiments, the species desorbed are the result of a surface reaction during the temperature ramp. 

In the end, mass spectrometry and ion techniques will continue to be powerful tools for the investigation of the structure, bonding, energetics, and reactivity of unusual organic molecules. New sophisticated techniques will continue to be developed and applied to interesting problems in physical organic chemistry. These studies, along with the continued improvements in computational methods (Chapter 9), provide means to obtain very detailed and accurate descriptions of chemical reactions. 

J. R. Chapman, "Computers in Hass Spectrometry", Academic Press, New York, NY, 1978. 

---