Electron bombardment, giving excited

All the methods used to evaporate metals for atom synthesis were developed originally for the deposition of thin metal films. The more important of these techniques are shown schematically in Fig. la-d. Most of the evaporation devices can be scaled to give amounts of metal ranging from a few milligrams per hour for spectroscopic studies to 1-50 gm/hour for preparative synthetic purposes. Evaporation of metals from heated crucibles, boats, or wires (Fig. la-c) generally gives metal atoms in their ground electronic state. Electronic excitation of atoms is possible when metals are vaporized from arcs, by electron bombardment, or with a laser beam (Fig. Id). The lifetime of the excited states of... 

In the following, we will focus our discussion on reactions occurring in clusters in which one chromophore is surrounded by the solvent molecules the reactions occur when the chromophore is excited in its first excited state or ionized. The interest of using a, chromophore within the cluster is that multiphoton ionization can be used in connection with mass spectrometry. In this case, the ionization is a soft process and the spectroscopy of the cluster can give information on the size of the cluster, which is excited and responsible for the reactive event. This assigment can be difficult in other methods (electron bombardment) due to fragmentation processes associated with ionization. 

Lamb and Retherford [81] proposed to make a beam of atomic hydrogen, and to excite it by electron bombardment. Most of the atoms in the 22S level, but not those in the 22P, levels, would live. long enough to reach a detector. A radiofrequency field of the correct frequency in the path of the atoms would induce transitions from 22 to one of the 22P levels. Decay of the latter would result in a reduction in the number of atoms detected, which would indicate radiofrequency resonance. We shall give here a brief account of the work and quote the results. Details of the experiments are given in a series of six papers [82], [83], [80], [84], [131], [30] and a review [79]. 

There are always four stages in any scheme of x-ray emission analysis. The excitation of characteristic radiation from the specimen by bombardment with high-energy photons, electrons, protons, etc. the selection of a characteristic emission line from the element in question by means of a wavelength or energy-dispersive spectrometer the detection and integration of the characteristic photons to give a measure of characteristic emission line intensity and finally, the conversion of the characteristic emission line intensity to elemental concentration by use of a suitable calibration procedure. 

Cathodoluminescence (CL) permits to give prominence to the layer sequence particularly white and off-white (e.g., pale yellow, cream colors) multilayered paint samples (see Figure 3(F)). It is the excitation of visible light or of radiation of adjacent wavelengths in semiconductors and insulators (e.g., inorganic pigments and extenders) when these are bombarded by electrons emitted from a cathode and accelerated in an electric field. 

Molecules in the upper atmosphere are constantly being bombarded by high-eneigy particles from the sun. As a result, these molecules either break up into atoms and/or become ionized. Eventually, the electronically excited species return to the ground state with the emission of light, giving rise to the phenomenon called aurora borealis (in the Northern Hemisphere) or aurora australis (in the Southern Hemisphere). 

Other, currently more specialist but of potential wide applicability, methods include the optical detection of quadrupole resonances—a sample is laser-excited to an electronically excited state, the return to the ground state is by phosphorescence the intensity of the phosphorescence is sensitive to whether or not concurrent microwave radiation matches an energy separation in some quadrupole-split intermediate state. Yet another method depends on correlations between successive p or y emissions from excited quadrupolar nuclei (where the excitation can be achieved by suitable nuclear bombardment). These do not exhaust the list of current developments—they have been chosen to illustrate the wide front on which new techniques are emerging. It is likely that because of these developments the future will see a wider use of NQR spectroscopy. It is also likely that the interpretation of the data will become more sophisticated. Traditionally, the experimental data have been interpreted to give the percentage ionic character of a bond. This is because, for example, in the CP ion all of the p orbitals are equally occupied whilst in CI2 the a bond, if composed of p orbitals only, corresponds to one electron in the p orbital of each chlorine atom, and so CP and Cl 2 differ in their resonant frequencies. Interpolation allows a value for the ionic character of a Cl-M bond to be determined from the chlorine resonance... 

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