Spectroscopic precision

In Equation 5.25 the ratio of G matrix elements has been obtained using a diatomic approximation (Gi/G/) = [(1/12) + (l/2)]/[(l/12) + (1/1)]. Although in the gas phase the frequency of each isotopomer can be measured to high precision, say 0.05 cm-1 or better, such precision is impossible in the liquid because of inherent broadening caused by intermolecular forces. Except in special cases band centers cannot be located to better than 0.5 cm-1, that limit is imposed by the nature of the liquid state. There is an identical uncertainty for each isotopomer, so spectroscopic precision is about... 

If it is possible at all to cedculate eigenvalues for many-electron problems exactly (in the sense of spectroscopic precision), then of course we have to start with the simplest, i.e. the helium problem. Here fair progress has been made in the past by the investigations of Kellner, Slater, and the present author. The results of this calculation can be summarised by the statement that the theory yields a ground term for helium which lies inside the error bars for direct measurements (by electron... 

Overall the Institute was outfitted with more modern and high-performance equipment than most universities at the time. In addition to providing for standard chemical procedures, the laboratory furnishings enabled researchers to pursue a number of specialized lines of research - such as studies of thermodynamic constants in the constant temperature rooms. The apparatus at the Institute conformed to the latest standards in physical chemistry research. For example, the electrical equipment was the best available at the time, offering not only alternating and direct current facilities but also a high-voltage installation in the machine hall. Similarly, the Institute possessed apparatus for research at the extremes of available gas pressures and at the limits of spectroscopic precision. ... 

EXAFS Extended X-ray absorption fine structure spectroscopy. A spectroscopic technique which can determine interatomic distances very precisely. 

Time-of-flight mass spectrometers have been used as detectors in a wider variety of experiments tlian any other mass spectrometer. This is especially true of spectroscopic applications, many of which are discussed in this encyclopedia. Unlike the other instruments described in this chapter, the TOP mass spectrometer is usually used for one purpose, to acquire the mass spectrum of a compound. They caimot generally be used for the kinds of ion-molecule chemistry discussed in this chapter, or structural characterization experiments such as collision-induced dissociation. Plowever, they are easily used as detectors for spectroscopic applications such as multi-photoionization (for the spectroscopy of molecular excited states) [38], zero kinetic energy electron spectroscopy [39] (ZEKE, for the precise measurement of ionization energies) and comcidence measurements (such as photoelectron-photoion coincidence spectroscopy [40] for the measurement of ion fragmentation breakdown diagrams). 

The homonuclear rare gas pairs are of special interest as models for intennolecular forces, but they are quite difficult to study spectroscopically. They have no microwave or infrared spectmm. However, their vibration-rotation energy levels can be detennined from their electronic absorjDtion spectra, which he in the vacuum ultraviolet (VUV) region of the spectmm. In the most recent work, Hennan et al [24] have measured vibrational and rotational frequencies to great precision. In the case of Ar-Ar, the results have been incoriDorated into a multiproperty analysis by Aziz [25] to develop a highly accurate pair potential. 

Spectroscopic methods for the deterrnination of impurities in niobium include the older arc and spark emission procedures (53) along with newer inductively coupled plasma source optical emission methods (54). Some work has been done using inductively coupled mass spectroscopy to determine impurities in niobium (55,56). X-ray fluorescence analysis, a widely used method for niobium analysis, is used for routine work by niobium concentrates producers (57,58). Paying careful attention to matrix effects, precision and accuracy of x-ray fluorescence analyses are at least equal to those of the gravimetric and ion-exchange methods. 

Precise kinetic electroanalytical data permit to describe quantitatively the kinetics of the whole process with a precision that has never been achieved before by patch-clamp techniques or spectroscopic near-field methods. This enables to investigate finely these events and to identify the exact physicochemical nature of all the individual physicochemical and biological factors which concur to produce vesicular release. 

In general the compounds have properties intermediate between those of the parent halogens, though a combination of aggressive chemical reactivity and/or thermal instability militates against the determination of physical properties such as mp, bp, etc., in some instances. However, even for such highly dissociated species as BrCl, precise molecular (as distinct from bulk) properties can be determined by spectroscopic techniques. Table 17.12 summarizes some of the more important physical properties of the... 

Thus in the presence of an excess of NH4+, which suppresses this forward reaction, and counteranions such as NOa" and C104, which have little tendency to coordinate, complexes such as [Hg(NH3)4] +, [Hg(L-L)2] + and even [Hg(L-L)3] + (L-L = en, bipy, phen) can be prepared. But, in the absence of such precautions, amino, or imino-compounds are likely to be formed, often together. Because of this variety of simultaneous reactions and their dependence on the precise conditions, many reactions between Hg and amines, although first performed by alchemists in the Middle Ages, remained obscure until the application of X-ray crystallography and, still more recently, spectroscopic techniques such as nmr, infrared and Raman. 

A. A. Miehelson (Chicago) optical precision instruments and the spectroscopic and metrological investigations carried out with their aid. 

An analysis of the Fourier Transform i.r. spectrum of PF around 946 cm-1 gave rise to nine spectroscopic constants for the Vg band and five for the Vg + v -v band which allowed calculation of the wavenumbers of the Vg band with a precision of 1 x 10-3 cm-1.11... 

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