Pulse gases

Figure 12. FITcct of the order of pulsed gases order for CO o itdatiwi reaction on Pt/ y AI203. The time profile of C02 was changed dynamically by the only 1ms of the dilTerencc of the timing of pulsing CO and 02...

Basically the pulsed Laval apparatus consists of one or two pulsed valves suppl3ung gas to a reservoir on which is moimted a Laval nozzle. The pulsed supersonic expansion is generated in the main chamber exhausted by a mechanical pump to pressures of 0.1 1 mbar. The uniformity of the Laval expansion is achieved by the appropriate background pressiue, consisting of the pulsed gases and a slip gas, which collimates the expansion along the axis of the gas flow. After a short transition time due to the valve cycle, the uniform supersonic flow is established in the chamber. As... 

Three different types of transient experiments can be performed using the TAP reactor. In single pulse experiments, which are often used, several ca. 100) lowsized ca. 10 —10 " molecules) pulses of a certain composition are injected into the micro-reactor. The pulsed mixture usually contains reactants and an inert gas, which serves as an internal standard. Due to the low amount of pulsed gases, the catalyst s state is not changed during these experiments. Therefore, they provide intrinsic kinetic information. 

The process of image forming in GDC can be divided into several stages formation of a latent electron-ion image, amplification of a latent image in a pulse gas discharge and production of a visible half-tone image. 

The apparatus and techniques of ion cyclotron resonance spectroscopy have been described in detail elsewhere. Ions are formed, either by electron impact from a volatile precursor, or by laser evaporation and ionization of a solid metal target (14), and allowed to interact with neutral reactants. Freiser and co-workers have refined this experimental methodology with the use of elegant collision induced dissociation experiments for reactant preparation and the selective introduction of neutral reactants using pulsed gas valves (15). Irradiation of the ions with either lasers or conventional light sources during selected portions of the trapped ion cycle makes it possible to study ion photochemical processes... 

It is more difficult to assign lines in laser systems which use polyatomic molecules in pulsed gas discharges 355) since here it is not always easy to decide whether the observed lines belong to transitions of the parent molecule or of dissociation products. 

Alternative methods of assisting the fluidization of difficult materials include the use of impellers in the bed to break up agglomerated particles, particularly to help initial fluidization in plug flow driers (Reay and Baker, 1985), and the use of a pulsed gas flow (Butcher, 1988). Bahu... 

The concentration C(xy t) of a pulsed gas as a function of time and axial position in a bed packed with a bipore distribution solid can be obtained by solving the following set of equations with appropriate initial and boundary conditions (1,2)... 

In the derivation of Equation 2 it was assumed that the adsorption isotherm is linear. This is generally the case in gas chromatography as a very small quantity of pulsed gas is injected. (Normally less than 4 cm3 of pulsed gas was injected into a column packed with 400 grams of adsorbents.)... 

Schmidt et al. [111] developed an atmospheric pressure laser ionization (APLI) source based on REMPI in pulsed gas expansions close to the inlet nozzle orifice (at high... 

Additional studies addressed the advantages of pulsed gas glow discharges coupled to the FT-ICR instrument. The FT-ICR technique requires quite low pressures in the analyzer cell to obtain the highest possible mass resolving power, since... 

The stainless steel micro reactor (figure 2) is constructed for catalyst pellet sizes of 0.175 to 0.20 mm. The reactor exit is connected via 0.9 m stainless steel capillary (i.d. 0.2 mm) to the analysing unit. The reactor and part of the capillary is mounted in an electric oven. A continuous stream of carrier gas passes the four way valve, then the catalyst bed, and flows via a stainless steel capillary into the detector. The carrier gas can be switched to pulse gas with the four way valve. The pressure in the reactor is determined by the resistance of flow in the capillary. The pressure difference between the carrier gas and the pulse gas is measured with a differential pressure detector. During the experiment the gas velocities of the carrier and the pulse gas are equal. The gasses are regulated by mass flow controllers. The gases used in the experiments were of a high purity. 

Figure 2 Schematic view of the apparatus used in studies of the steric effects in gas-surface scattering. A detail of the crystal mount with die orientation rod at 1 cm in front of the surface is shown in die right hand corner. A detailed drawing of the hexapole state selector is given below the main figure. The voltage is applied to die six small rods indicated by an arrow. Key Q quadrupole mass spectrometer R Rempi detector M, crystal manipulator SI, beam source for state selected molecules H electric hexapole state selector C mechanical beam chopper V pulsed gas source S2, continuous molecular beam source. From Tenner et al. [34].

A quite different approach to radiofrequency, microwave and infrared spectroscopy is that known as Fourier transform (FT) spectroscopy. As we shall see, this method of recording the spectra of transient molecular species is particularly appropriate in combination with the use of pulsed gas nozzles. For this reason it has proved to be a powerftd technique for the study of weakly bound dimer complexes formed in supersonic gas expansions. It has, however, also been used for the study of diatomic molecules, both... 

Before the invention of lasers in 1960 (Maiman), radiation emitted by the mercury arc, especially at 435.8 and 404.7 nm, has been u.sed for exciting Raman spectra (Brandmiiller and Moser, 1962). Today, most types of lasers ( continuous wave (cw) and pulsed, gas, solid state, semiconductor, etc.), with emission lines from the UV to the NIR region, are used as radiation sources for the excitation of Raman spectra. Especially argon ion lasers with lines at 488 and 515 nm are presently employed. NIR Raman spectra are excited mainly with a neodymium doped yttrium-aluminum garnet laser (Nd YAG), emitting at 1064 nm. 

Laaer-Dsaorptfon Maaa Spaclronetry. Thick Tilms of pure or mixed molecular carbon are d osited high-vacuum chamber (Figure 2) within a short no assembly, which in turn mounu on the faceplate of a pulsed gas valve. The rod is continuously... 

SOME MODIFICATIONS OF PULSE GAS CHROMATOGRAPHIC METHODS OF DETERMINING KINETIC CHARACTERISTICS... 

Bochkov, VD, Korolev, Yu.D (2000), Pulsed Gas-Discharge Commutation Devices, in Encyclopedia of Low-Temperature Plasma, Fortoy VE. (ed.), vol. 4, Nauka (Science), Moscow, p. 203. 

Pulsed gas flow Variable gas temperature Mechanically assisted fluidization (vibration/agitation)... 

Variable gas flow/pulsed gas flow Variable gas temperature Drying pastes, slurries using inert media Moving spout (rotation, oscillation) Combined convection and conduction Two-dimensional, annular, hexagonal, etc. 

The time profile of the laser pulse is not only determined by the amplification per round trip G t) (Vol. 1, Sect. 5.2) but also by the relaxation times t,-, Xk of the upper and lower laser levels. If these times are short compared to the rise time of the pump pulse, quasi-stationary laser emission is reached, where the inversion AN(t) and the output power FL(r) have a smooth time profile, determined by the balance between pump power Pp t), which creates the inversion, and laser output power Fl(0. which decreases it. Such a time behavior, which is depicted in Fig. 6.1a, can be found, for instance, in many pulsed gas lasers such as the excimer lasers (Vol. 1, Sect. 5.7). 

Fig. 3.9 Structure of A[Cu3((jl3-OH)( X3—4-carboxypyrazolato)3] (A = NH or Et3NH+) and the results of variable-temperature pulse gas chromatography experiments based on an equimo-lecular C2H2/N2/CH4/CO2 gas mixture passing through a chromatographic column packed with this material. Reprinted from Ref. [57] Copyright 2011, with permission from Elsevier...

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