Electronic fundamentals, mass sensitive

In the past decade, as systems have become simpler to operate, mass spectrometry (MS) has become increasingly popular as a detector for GC. Of all detectors for GC, mass spectrometry, often termed mass selective detector (MSD) in bench-top systems, offers the most versatile combination of sensitivity and selectivity. The fundamentals of MS are discussed elsewhere in this text. Quadrupole (and ion trap, which is a variant of quadrupole) mass analyzers, with electron impact ionization are by far (over 95%) the most commonly used with GC. They offer the benefits of simplicity, small size, rapid scanning of the entire mass range and sensitivity that make an ideal detector for GC. 

Recent ab initio calculations have attempted to probe the fundamental source of the reversal of H/D preference in ionic as compared to neutral systems, using water as a test base. A harmonic analysis of the potential energy surface of the water dimer, computed with a 6-31G basis set, indicates that the preference for D in the bridging site can be explained in a manner similar to that described earlier for HF - HF. The frequency of the bending motion of the bridging atom is sensitive to its mass this effect leads to a lower vibrational energy of some 0.2 kcal/mol when the heavier D undergoes this motion. The computations indicated that electron correlation has little effect upon this conclusion, even its quantitative aspects. While the treatment was purely harmonic in nature, other calculations have indicated that anharmonicity effects yield very little distinction between one isotopomer and the next. 

In this chapter, we describe the application of precision molecular spectroscopy to the study of a possible temporal and spatial variation of the fundamental constants. As we will show below, molecular spectra are mostly sensitive to two such dimensionless constants, namely the fine-structure constant a = e jhc and the electron-to-proton mass ratio p, = m jm (note that some authors define p as an inverse value, i.e., the proton-to-electron mass ratio). At present, NIST lists the following values of these constants [1] a = 137.035999679(94) and p- = 1836.15267247(80). 

The hydrogen molecular ion is very attractive for fundamental studies because of its simplicity and the feasibility of its cooling and trapping (compare with Chapter 18 by Roth and Schiller). The use of hJ and HD+ ions for the study of the time variation of the electron-to-proton and theproton-to-deuteron mass ratios p = me/fftp and mp/md has been suggested in Refs. [86] and [87]. Because of the anharmonicity of the ion s potential, the ratio of the two vibrational transitions with very different vibrational quantum numbers is p-dependent [86]. As a result, there is no enhancement of the relative sensitivity here, but the lines are very narrow and high-precision measurements are possible using frequency combs. 

Ions and radicals are transient species which are not readily accessible to conventional techniques for spectroscopic characterization. There are essentially three problems to be overcome-the production in sufficient concentration, the availability of a sensitive technique enabling their IR or electronic spectra to be recorded and the ability to identify the observed spectral features. The involvement of mass-selection not only leads to the solution of the last problem, but enables methods based on particle detection -fragment ions, electrons and photons - to be incorporated. The aim of the spectroscopic studies is, on the one hand, to provide a fingerprint of the species by its vibrational or electronic spectrum, enabling its identification in various terrestrial and space environments, and on the other hand, the spectroscopic analysis leads to information on geometric structures, force fields and fundamental interactions. 

Room-temperature ionic liquids (RTILs) are intrinsic ionic conductors which have been successfully employed as nonflammable/nonreactive electrolytes in a range of electrochemical devices, including dye-sensitized solar cells [1,2], lithium batteries [3], fuel cells [4], and supercapacitors [5]. The quantification of mass transport is of interest in any solvent, particularly those employed in electrochemical devices, as it affects the ultimate rate/speed at which the device can operate. The diffusivity or diffusion coefficient (D) of a redox active species, along with other thermodynamic parameters such as the bulk concentration (c) and the stoichiometric number of electrons (n) that are of fundamental significance in any study of an electrode reaction, can be determined experimentally using a range of electroanalytical techniques [6], As with any analytical method, the ideal electroanalytical technique for parameter characterization should be accurate, reproducible, selective, and robust. In many respects voltammetric methods meet these requirements, since they can be... 

The cross section of a bar is proportional to its mass, thus there are efforts to build a 100-ton spherical resonant de-teetor, with high sensitivity and omnidirectional response. The sphere must be equipped with several transducers to detect the fundamental modes the quadrupole modes and the monopole mode (not sensitive to gravitational waves). Efforts are also being devoted to developing more efficient electronics systems (transducers and amplifiers) to achieve better sensitivity. Another major improvement foreseen is the increase of the bandwidth from the current few hertz to several tens of hertz. In this way, coincident runs could allow the determination of source position. 

Piezoelectric acoustic wave device such as the quartz crystal microbalance offer many attractive features as vapor phase chemical sensors small size, ruggedness, electronic output, sensitivity, and adaptability to a wide variety of vapor phase analytical problems. The QCM is based on a piezoelectric quartz substrate coated with keyhole pattern electrodes on opposite surfaces on the crystal. Mass changes Am (in g) per face of the QCM cause proportional shifts Af of the fundamental resonance frequency F, according to... 

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