Cells, gas

Gas cells may be considered a special form of transmission cell. The difference is primarily in the construction of the body of the cell and its extended pathlength. In essence, a traditional gas cell (short path length) is a tube (with filling ports) with windows mounted and sealed at both ends. Like liquid cells, gas cells are available in demountable (removable windows) and permanent formats (bonded windows). Materials of construction can be important, especially if corrosive gases or vapors are studied. The most inexpensive cells feature glass tubular bodies, and these are ideal for many sample types. For a more rigid construction, cell bodies made from stainless steel, Monel, and Hastelloy C are available. 

Temperature is also an important parameter, and the heating of cells may be required for samples that condense at ambient temperatures. Various forms of heated gas cells are available for such applications. If the cell is heated, it is necessary to record the temperature because this will impact the quantitative aspects of any gas-phase measurement (because of 

It is essential to ensure that no condensed material is formed on the internal optical surfaces prior to use. For some samples, it may be necessary to use the cell at elevated temperature to prevent condensation from occurring. If this is the case, it is important to be certain that the cell is constructed for operation at higher than ambient temperatures. This includes the materials used for construction (such as bonding materials for the internal optics) as well as the ability of the cell to retain optical throughput (due to dimensional changes). 

Standard commercially available gas cells can be divided into two main classes. Glass-body cells and metal-body cells. Both classes of 

These cells can be evacuated to less than 1 mm Hg pressure, but cannot be filled to more than one atmosphere pressure. Excess pressure inside the cells will tend to break the seals holding the windows to the body and cause leaks. The cells also can be converted for use at elevated temperatures by wrapping them with heating tape. When heating the cell, do not increase the pressure above one atmosphere. 

Metal-Body Cells. It is possible to get cells similar to those above with metal instead of glass bodies. Usually, however, the term metal body implies cells of longer path length, or high-pressure cells. Windows are held in place with retainer rings. 

Metal-body cells are equipped with either valves or hose nipples to allow evacuation, filling, cleaning, or flushing. The hose nipples can be replaced by valves, if the operator so desires. 

Care must be used in deciding what samples to run in these cells, or corrosion of the metal bodies, mirror mounts, or mirror surfaces may result. Another frequently encountered problem is the adsorption of sample by the cell walls. The current practice of lining the cell with a resin or plastic has reduced but not eliminated this problem. 

Preparation of the Electrodes.—As electrodes, oblong strips of platinum foil may be used. The foil is welded to a piece of platinum wire, which is then sealed into a glass tube and 

Before the electrodes are platinized, they should be cleaned by treatment for 5 minutes with a warm solution of potassium bichromate acidified with sulphuric acid, and then well washed with distilled water. After being platinized, the electrodes may be freed from occluded chlorine by immersion for-quarter of an hour in a mixed solution of ferrous and ferric salts acidified with sulphuric add. They are then thoroughly washed with.distilled water, and kept in distilled water till required for use. 

When platinum foil is used for the electrodes, many hours may be required for the equilibrium between the gas and the solution, and therefore for a constant electrical potential, to be established. It is better therefore to employ thin films of platinum on glass. These electrodes can be prepared in the following manner — 

A iJiece of glass tubing (preferably of Jena glass), of length and diameter adapted to the electrode vessel to be employed, is drawn out as shown in Fig. 82 the end of the narrow portion A being sealed, while the other end of the tube is left open. By means of a small brush, coat 

If the deposit of platinum is too thin, another maybe put on in the same manner, after allowing the tube to cool. When a satisfactory coating has been obtained, seal off the tube at a. 

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LIF has been used to study state-selected ion-atom and ion-molecule collisions in gas cells. Ar reactions with N2 and CO were investigated by Leone and colleagnes in the 1980s [13, 14] and that group has... 

It is also possible to measure microwave spectra of some more strongly bound Van der Waals complexes in a gas cell ratlier tlian a molecular beam. Indeed, tire first microwave studies on molecular clusters were of this type, on carboxylic acid dimers [jd]. The resolution tliat can be achieved is not as high as in a molecular beam, but bulk gas studies have tire advantage tliat vibrational satellites, due to pure rotational transitions in complexes witli intennolecular bending and stretching modes excited, can often be identified. The frequencies of tire vibrational satellites contain infonnation on how the vibrationally averaged stmcture changes in tire excited states, while their intensities allow tire vibrational frequencies to be estimated. 

As described above, classical infrared spectroscopy using grating spectrometers and gas cells provided some valuable infonnation in the early days of cluster spectroscopy, but is of limited scope. However, tire advent of tunable infrared lasers in tire 1980s opened up tire field and made rotationally resolved infrared spectra accessible for a wide range of species. As for microwave spectroscopy, tunable infrared laser spectroscopy has been applied botli in gas cells and in molecular beams. In a gas cell, tire increased sensitivity of laser spectroscopy makes it possible to work at much lower pressures, so tliat strong monomer absorjDtions are less troublesome. 

Samples were prepared by using a vacuum manifold to fill the gas cell. After measuring the total pressure, the absorbance of the sample at 2170 cm- was measured. Results are reported as %CO (Pco/ftot)- Five exhaust samples were obtained from a 1973 coupe, yielding the following results... 

Alternatively, ions of any one selected m/z value can be chosen by holding the magnetic field steady at the correct strength required to pass only the desired ions any other ions are lost to the walls of the instrument. The selected ions pass through the gas cell and are detected in the singlepoint ion collector. If there is a pressure of a neutral gas such as argon or helium in the gas cell, then ion-molecule collisions occur, with decomposition of some of the selected incident ions. This is the MS/MS mode. However, without the orthogonal TOF section, since there is no further separation by m/z value, the new ions produced in the gas cell would not be separated into individual m/z values before they reached the detector. Before the MS/MS mode can be used, the instrument must be operated in its hybrid state, as discussed below. 

The hybrid can be used with El, Cl, FI, FD, LSIMS, APCI, ES, and MALDI ionization/inlet systems. The nature of the hybrid leads to high sensitivity in both MS and MS/MS modes, and there is rapid switching between the two. The combination is particularly useful for biochemical and environmental analyses because of its high sensitivity and the ease of obtaining MS/MS structural information from very small amounts of material. The structural information can be controlled by operating the gas cell at high or low collision energies. 

Collision of an ion with an inert gas molecule leads to some deflection in the ion trajectory. After several collisions, the ion could have been deflected so much that it no longer reaches the detector. This effect attenuates the ion beam as it passes through the gas cell, leading to loss of instrumental sensitivity. An attenuation of 50 to 70% is acceptable and is not unusual in practice. 

The primary advantage of MCP is to create a large number of gas cells rapidly during mixing. These gas cells serve as nuclei for a greater expansion later in the oven. MCP also finds many uses in the products in which fast release of carbon dioxide and a low bench action are requited. Examples are pancake mixes, cookie mixes, and angel food cakes. The milling industry uses MCP in the manufacture of phosphated flour. 

Gas-kalk, m. gas linxe. -kammer, /. gaa chamber, -kampf, m. gas warfare, chemical warfare. -kampffiasche, /. a small gas cylinder for cloud gas attacks, -kampfstoff, m. war gas. -kette, /. (Elec.) gas cell. 

In the case of gas cells it is more convenient to substitute partial pressures for concentrations in the equation ... 

Gas, cells, 464, 477, 511 characteristic equation, 131, 239 constant, 133, 134 density, 133 entropy, 149 equilibrium, 324, 353, 355, 497 free energy, 151 ideal, 135, 139, 145 inert, 326 kinetic theory 515 mixtures, 263, 325 molecular weight, 157 potential, 151 temperature, 140 velocity of sound in, 146 Generalised co-ordinates, 107 Gibbs s adsorption formula, 436 criteria of equilibrium and stability, 93, 101 dissociation formula, 340, 499 Helmholtz equation, 456, 460, 476 Kono-walow rule, 384, 416 model, 240 paradox, 274 phase rule, 169, 388 theorem, 220. Graetz vapour-pressure equation, 191... 

In the documents, six different meso-levels are found. For example, dough contains gas cells (10 m), enclosed by walls made up of a matrix with embedded... 

Co concentration was determined by spectrophotometer (Varian Cary 500) at 692 nm wave length, with the sample diluted with a 9 mol/L concentrated HCl solution. NO content in gas phase was obtained by an on-line Fourier transform infrared spectrometer (Nicolet E.S.P. 460 FT-IR) equipped with a gas cell and a quantitative package, Quant Pad. 

Those fixed-angle measurements reported to date have all used either a heated effusive inlet, or heated gas cell for sample admission [55, 56, 61, 62, 65]. Probably the higher sample number densities these sources generate, compared to a supersonic beam source, provides some compensation for the reduced collection efficiency in the fixed-angle measurement. 

The cancellation of gas phase spectral features using the "half plate design Is far superior to methods Involving a second gas cell placed In the reference beam. This Is because the gas density and Its rotational state population will differ In the two cells for different sample (and therefore gas) temperatures. For high sensitivity measurements, these effects can be difficult to handle using two cells. 

The collected sample at -196°C was isolated from the flow of the GC s helium gas stream and then the loop was warmed to ambient temperature for GC-mass spectroscopic analyses. The gas cell, which contained the isotopic CO2 and the C2Hg standard in helium at one atmosphere, was placed in the injection helium flow of the GC-mass spectrometer for ten minutes, before the mini-switching valve was turned to inject the vapor contents into the instrument. After three minutes, the CO2 peak eluted. The superimposed peaks were sampled ten times during their elution and the relative isotopic quantities of - C02 C02 and C02 were determined. 

We consider a general dissipative environment, using a three-manifold model, consisting of an initial ( ), a resonant ( r ), and a final ( / ) manifold to describe the system. One specific example of interest is an interface system, where the initial states are the occupied states of a metal or a semiconductor, the intermediate (resonance) states are unoccupied surface states, and the final (product) states are free electron states above the photoemission threshold. Another example is gas cell atomic or molecular problems, where the initial, resonant, and final manifolds represent vibronic manifolds of the ground, an excited, and an ionic electronic state, respectively. 

Fig. 4. Schematic cross section of the Northwestern flow gas cell. Fe(CO)5 enters through the center port, Ar purge gas through ports by the windows. [Reproduced with permission from Ouderkirk et al. (75).]...

For sensing applications, high bending losses restrict the applicability as (flexible) light pipes. Practical applications are mostly restricted to gas cells, where the hollow waveguide acts as a compact multi-reflection cell to increase the sensitivity in comparison to single-pass cells. 

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