Discharges, electrical

One distinguishes here between the so-called silent discharges at atmospheric pressure and glow discharges at reduced pressure. Other discharge types such as arcs are not considered here, since in those cases the specific discharge effects are masked by thermal ones. 

Silent discharges are obtained in a Siemens ozonizer, which is a system of two concentric tubes. The gas flows through the annulus (see Part II, section on Ojgrgen and Ozone). 

Aluminum foil Is used for electrodes whenever possible. It is the least dust-forming material. In the case of halogens, water-cooled iron tubes (Schwab s apparatus Cll]) must be used. The discharge tube is approximately 20 mm. I. D. and is enlarged at the end, where a 40-mm.-thick Al electrode is placed. If the electrodes are sufficiently close to the walls, the tube can carry a current of 200-300 ma. without special cooling. For higher currents a fan is 

The many successful simulation experiments indicate that electrical discharges on prebiotic Earth may have been involved in the synthesis of biomolecules. However, we simply do not know how important they actually were Studies of energy 

the estimates for the rates of the prebiotic synthesis of biomolecules also need a drastic downward correction the hypothetical primeval soup then becomes much thinner  

Shock waves can be natural in origin, for example, lightning, volcanic explosions or meteorite impacts. But human activity can also generate shock waves, for example in chemical or nuclear explosions. On the positive side, shock waves can reduce human suffering when used in shock wave lithotripsy (a method for fragmentation of kidney stones and gallstones). 

Physically speaking, shock waves are compaction waves with a vertical shock front, which occur in supersonic fluxes or as described above the pressure reaches a maximum value and then falls rapidly towards zero. Shock waves can also occur in space, which is almost free of matter, via interactions of electrical and magnetic fields (Sagdejev and Kennel, 1991). 

More than 40 years ago, Hochstim (1963) showed that organic products are formed in simulation experiments using shock waves. However, no information on yields is available. Using shock wave heating of a reducing gas mixture, Bar-Nun et al. (1970) were able to obtain relatively high yields of amino acids. However, when the work was later repeated, it turned out that the authors had been too optimistic the yields were lower by a factor of 30 (Bar-Nun and Shaviv, 1975). 

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Boron sub-iodide, B2I4, is prepared by the action of an electrical discharge on BI vapour. 

Selenium (rioxide, SeOj. M.p. 120°C. Formed Se vapour plus O2 in electric discharge. it is while and gives H2Se04 with water. 

Since this state is so low in energy, it is likely to be populated in the F atom beams typically used in scattering experiments (where pyrolysis or microwave/electrical discharges are used to generate F atoms), so the issue of its reactivity is important. The molecular beam experiments of Lee [43] and Toennies [45] showed no evidence for... 

Larger molecules generally caimot be studied in quite the same way, as an electric discharge merely breaks them up into smaller molecules or atoms. In such a case excited states are usually produced by optical excitation using light of the same or higher energy. Many modem fluorimeters are made with two... 

Plenary 9. J W Nibler et al, e-mail address niblerj chem.orst.edu (CARS and SRS). High resolution studies of high lymg vibration-rotational transitions in molecules excited in electrical discharges and low density monomers and clusters in free jet expansions. Ionization detected (REMPI) SRS or IDSRS. Detect Raman... 

Beams of metal atoms have been prepared by many researchers tlirough thennal vaporization from a heated cmcible. An example of such a source, employed for the generation of beams of alkaline earth atoms, is described by Irvin and Dagdigian [H]. By striking an electrical discharge within this source, beams... 

Figure C2.13.3. Schematic illustrations of various electric discharges (a) DC-glow discharge, R denotes a resistor (b) capacitively coupled RF discharge, MN denotes a matching network (c), (d) inductively coupled RF discharge, MN denotes matching network (e) dielectric barrier discharge.

The deposition of organic films by plasma polymerization is an important application of non-thennal plasmas 1301. Plasma polymers are fonned at the electrodes and the walls of electrical discharges containing organic vapours. Oily products, soft soluble films as well as hard brittle deposits and powders are fonned. The properties of plasma... 

MoTaggart F K 1967 Plasma Chemistry in Electrical Discharges (Amsterdam Elsevier)... 

There are many compounds in existence which have a considerable positive enthalpy of formation. They are not made by direct union of the constituent elements in their standard states, but by some process in which the necessary energy is provided indirectly. Many known covalent hydrides (Chapter 5) are made by indirect methods (for example from other hydrides) or by supplying energy (in the form of heat or an electric discharge) to the direct reaction to dissociate the hydrogen molecules and also possibly vaporise the other element. Other known endothermic compounds include nitrogen oxide and ethyne (acetylene) all these compounds have considerable kinetic stability. 

Small quantities of ozone are produced when oxygen and air are subjected to an electrical discharge and it is, therefore, found in the neighbourhood of working electrical machines. Probably a small quantity of atomic oxygen is initially produced most of this recombines quickly to give oxygen, Oj, but a few atoms react to form ozone ... 

Ozone is normally produced by the use of a silent electrical discharge and a number of ozonisers have been produced. Brodie s apparatus is shown in outline in Figure 10.2. 

To increase the number of ions, a plasma or corona discharge is produced in the mist issuing from the capillary. The electrical discharge induces more ionization in the neutrals accompanying the few thermospray ions. This enhancement increases the ionization of sample molecules and makes the technique much more sensitive to distinguish it from simple thermospray, it is called plasmaspray. 

All methods of plasma production require some electrons to be present as electric-discharge initiators. For a plasma torch, the initiating electrons are introduced from a piezoelectric spark directed into argon gas flowing in the interval between two concentric quartz tubes. 

The major methods used for vaporization (ablation) include lasers, electrically heated wires, or sample holders and electrical discharges (arcs, sparks). 

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