Experimental methods spectrometry

Historically, some of those approaches have been developed with a considerable degree of independence, leading to a proliferation of thermochemical concepts and conventions that may be difficult to grasp. Moreover, the past decades have witnessed the development of new experimental methods, in solution and in the gas phase, that have allowed the thermochemical study of neutral and ionic molecular species not amenable to the classic calorimetric and noncalorimetric techniques. Thus, even the expert reader (e.g., someone who works on thermochemistry or chemical kinetics) is often challenged by the variety of new and sophisticated methods that have enriched the literature. For example, it is not uncommon for a calorimetrist to have no idea about the reliability of mass spectrometry data quoted from a paper many gas-phase kineticists ignore the impact that photoacoustic calorimetry results may have in their own field most experimentalists are notoriously unaware of the importance of computational chemistry computational chemists often compare their results with less reliable experimental values and the consistency of thermochemical data is a frequently ignored issue and responsible for many inaccuracies in literature values. 

E. Heinzle, K. Furukawa, I. J. Dunn, and J. R. Bourne, Experimental methods for online mass spectrometry in fermentation technology, Bio/Technol. 1, 181-188 (1983). 

Mass spectrometry is one of the experimental methods for determining bond dissociation enthalpies. The mass spectrometer can provide a measure of the appearance potential for a given reaction, that is, the threshold energy necessary to produce a particular set of particles. The appearance potential for the following reaction of H2,... 

In the present review, a new variation on an existing experimental method will be used to show how accurate unimolecular dissociation rate constants can be derived for thermal systems. For example, thermal bimolecular reactions are amenable to study by use of several, now well-known, techniques such as (Fourier transform) ion cyclotron resonance spectrometry (FTICR), flowing afterglow (FA), and high-pressure mass spectrometry (HPMS). In systems where a bimolecular reaction leads to products other than a simple association adduct, the bimolecular reaction can always be thought of as containing a unimolecular... 

Essentially, any technique applicable to the measurement of physicochemical properties of compounds may be considered for the study of reaction rates, and it is up to the imagination of the researcher to exploit the principles behind the technique and devise an experimental method. A number of extremely useful electrochemical techniques are covered in Chapter 6, and Chapter 8 includes a very promising new method combining calorimetric and FTIR measurements. Mass spectrometry, a field in constant development and with an abundant literature, is ideally suited for the study of wide-ranging reaction types in the gas phase, including those related to atmospheric investigations, but is beyond the scope of this chapter. 

MacKenzie, I.K. (1983). Experimental methods of annihilation time and energy spectrometry. In Positron Solid-State Physics, Proc. Int. School of Physics Enrico Fermi , Course 83, eds. W. Brandt and A. Dupasquier (North-Holland) pp. 196-264. 

The different emission products which are possible after photoionization with free atoms lead to different experimental methods being used for example, electron spectrometry, fluorescence spectrometry, ion spectrometry and combinations of these methods are used in coincidence measurements. Here only electron spectrometry will be considered. (See Section 6.2 for some reference data relevant to electron spectrometry.) Its importance stems from the rich structure of electron spectra observed for photoprocesses in the outermost shells of atoms which is due to strong electron correlation effects, including the dominance of non-radiative decay paths. (For deep inner-shell ionizations, radiative decay dominates (see Section 2.3).) In addition, the kinetic energy of the emitted electrons allows the selection of a specific photoprocess or subsequent Auger or autoionizing transition for study. 

Abstract. In the paper we consider the problems with moving bound that model the kinetics of hydrogen desorption from hydrides of metals. Change of phase, desorption processes and size reduction effect are taken into consideration. Equations are derived at various assumptions for the experimental method of thermal desorption spectrometry. As the high-temperature TDS-spectra peaks are considered, the diffusion may be assumed to be fast. Therefore ordinary differential equations are sufficient. We present the results of numerical experiments for the models with bulk and surface desorption. 

The stereochemistry of enolisation has been mostly examined in cyclic systems where the relative positions of the enolisable hydrogen atoms are fixed. Over the last decade, these studies have benefited from important improvements in the experimental methods, namely mass spectrometry and nmr spectroscopy. Of great interest is the comparison of the relative mobilities of diastereoisomeric axial and equatorial protons from ketones in the cyclohexane series. Indeed, since axial a(C—H) bonds of rigid cyclohexanones are closer than equatorial a(C—H) bonds to the desirable conformation in which the breaking C—H bond is perpendicular to the direction of the C=0 bond, it can be expected that the axial a(C—H) bond-breaking is easier than that of the equatorial one. 

For the investigation of meteorites various experimental methods are applied, in particular mass spectrometry, neutron activation analysis, measurement of natural radioactivity by low-level coimting and track analysis. The tracks can be caused by heavy ions in cosmic radiation, by fission products from spontaneous or neutron-induced fission and by recoil due to a decay. Etching techniques and measurement of the tracks give information about the time during which the meteorites have been in interstellar space as individual particles (irradiation age). 

It has been mentioned in Ch. 6 that these transfers of H-atoms are poorly known. They consequently need an important effort before they can be understood, so that such related quantities as typical times, numbers of participating H2O molecules, effect of temperature, etc. become known. Such methods as IR spectrometry, both conventional and nonlinear time-resolved, will certainly be the basic experimental methods to precisely observe these transfers. Theoretical accompanying developments are likely to be also useful. On which H-bonded systems will these mechanisms be observed No precise answer can be given, but recent hydration experiments, such as that of HA described above, may already give... 

The study of gaseous metal halide complexes is of fundamental interest for the chemistry of coordination compounds. In addition, gaseous metal halide species are of practical importance for material science and technical applications. These practical aspects are reported briefly in the recent review by Schafer [425] and in detail in the book by Hastie [428]. The potential of enhanced vapor phase material transport is for example an important practical aspect and has been described in the monograph by Schafer [437]. It is of interest for metal halide lamps, chemical vapor deposition, and metallurgical processes. The practical significance of complexation for metal halide lamps and the experimental methods used in addition to Knudsen effusion mass spectrometry for the study of metal halide vapors are reported in the recent review article by Hilpert [438]. 

Investigations of the acidity of specific surface sites may be accomplished by studies coordinated with spectroscopic methods, such as infrared (JR) spectroscopy, nuclear magnetic resonance (NMR) spectroscopy, or mass spectrometry (MS). Surface characterization with Fourier transform infrared (FTIR) spectroscopy can provide quantitative results with experimental methods that are easily performed. However, the transmission sampling techniques traditionally employed for infrared studies may introduce experimental artifacts on the analyzed surface (10,... 

Several methods exist that allow the determination of the standard enthalpies of formation of the ionic species. The reader is referred to two recent rigorous and detailed chapters by Lias and Bartmess and Ervin. The vast majority of the experimental data reported here are obtained by means of Fourier transform ion cyclotron resonance spectroscopy (FT ICR), high-pressure mass spectrometry (HPMS), selected ion flow tube (SIFT), and pulsed-field ionization (PFI) techniques, particularly pulsed-field ionization photoelectron photoion coincidence (PFI-PEPICO). All these experimental techniques have been examined quite recently, respectively, by Marshall, Kebarle, B6hme," ° Ng" and Baer. These chapters appear in a single (remarkable) issue of the International Journal of Mass Spectrometry. An excellent independent discussion of the thermochemical data of ions, with a careful survey of these and other experimental methods, is given in Ref. 37. 

The kinetics of formation and disintegration of micelles has been studied for about thirty years [106-130] mainly by means of special experimental methods, which have been proposed for investigation of fast chemical reaction in liquids [131]. Most of the experimental methods for micellar solutions study the relaxation of small perturbations of the aggregation equilibrium in the system. Small perturbations of the micellar concentration can be generated by either fast mixing of two solutions when one of them does not contain micelles (method of stopped flow [112]), or by a sudden shift of the equilibrium by instantaneous changes of the temperature (temperature jump method [108, 124, 129, 130]) or pressure (pressure jump method [1, 107, 116, 122, 126]). The shift of the equilibrium can be induced also by periodic compressions or expansions of a liquid element caused by ultrasound (methods of ultrasound spectrometry [109-111, 121, 125, 127]). All experimental techniques can be described by the term relaxation spectrometry [132] and are characterised by small deviations from equilibrium. Therefore, linearised equations can be used to describe various processes in the system. 

The range of experimental methods and data acquisition techniques for stress mass spectrometry experiments provide a way to obtain a great amount of data on the volatile compounds evolved from polymeric samples when subjected to a mechanical load. These data provide information concerning the events occurring in the polymer which produce the evolved volatile compounds. 

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