Effusion molecular

Other than the earlier work reviewed by Ashfold et al. (3), only three studies on the photodissociation dynamics have been reported for this molecule (153,154,158). The first study reported the quantum state distribution of the CN radical obtained in an effusive molecular beam and in a static gas cell, while the second study reported the observations in a pulsed molecular beam. The dynamics remains the same despite the fact that the initial internal state distribution of the C1CN molecule changes. This of course shows that hot bands are not important in the photodissociation of this molecule at this wavelength. 

The essential elements.of the experiment are a) an effusive molecular beam source, b) inhomogeneous deflecting electric polefaces, c) surface ionization detector, capable of translation in order to obtain the deflected beam pattern. 1, 2, are the distance from the source to the front of the polefaces, the length of the polefaces and the distance from the back of the polefaces to the detector, respectively. A general review of deflection methods for determining polarizabilities is given by Miller and Bederson (8). 

It is obvious that n and have to be determined accurately, n is usually determined by measuring the pressure, for example with a capacitance manometer such as a baratron, taking care to allow for temperature differences between the gas cell and the measuring region (Blaauw et al, 1980). Usually one has an effusive molecular flow through the entrance and exit apertures, which leads to large density gradients in the gas, and the product mf in the exponent of (2.10) has to be replaced by... 

A special feature of this system is the gas-phase sampling by an effusive molecular beam leading to a collision-free transfer of the sample into the analysis chamber. Liquid nitrogen cooled traps in the differential pumping stage and around the ion source of the TOF-MS serve to ensure for a low background. " ... 

Benzene ions are produced in an effusive molecular beam inside the acceleration field of a reflectron time-of-flight mass spectrometer /12/. (see Fig. 3). Laser 1 is tuned to the frequency of the 6 i or 60116 -1 band and produces, via a resonance-enhanced two photon absorption, state- and energy-selected benzene cations. 

A collimated effusive molecular beam with a rectangular density profile behind the collimating aperture has a thermal velocity distribution at T = 500 K. Calculate the intensity profile a oS) of an absorption line, centered at two for molecules at rest, if the beam of a weak tunable monochromatic laser crosses the molecular beam under 45° against the molecular beam axis... 

Fig. 2.2 Velocity distribution from effusive molecular beam (dot) and supersonic molecular beam solid line). Both curves are normalized to unity at the most probable velocity and are for helium at a reservoir temperature of 300 K. The curve for the supersonic molecular beam assumes the speed ratio v/Av =10...

From the maximum of the shifted absorption profile the most probable velocity Vp can be deduced [10.17]. Figure 10.6b illustrates the measurement of velocity distributions of Na molecules in specified quantum states at different oven temperatures. The narrowing of the velocity distribution with increasing oven temperature and the increase of the most probable velocity Vp characterize the transition region from a thermal effusive molecular beam to a supersonic beam. The velocity distribution in the supersonic beam can be described by... 

To our knowledge [63], there is no way to precisely control the temperature with the current experimental (e, 2e) setup which Liu et al. [45] used at Tsinghua University (Beijing, China) for their experiments on W(CO)g, a set-up which employs effusive molecular beams. In contrast with experiments based on free expansions in supersonic jets, it is usually assumed that the relatively high pressure in the collision cell ensures a full randomization of molecular motions, and thermal equilibrium therefore with the environment (298 K). Therefore, we wish to consider both the estimated experimental and standard room temperatures in our BOMD analysis. At last, the role played by nuclear dynamics in the final ionized state is also tentatively investigated. In this purpose, we revise before aU (theory section) how electron momentum distributions may vary in response to a change in the molecular geometry induced by ionization. 

As a consequence of these simple deductions, Graham s experiments c effusion through an orifice came to be regarded as one of the earliest direct experimental checks on the kinetic theory of gases. However, a closer examination of his experimental conditions reveals that this view is mistaken. As mentioned earlier, his orifice diameters ranged upwards from 1/500 in., while the upstream pressure was never very much less thai atmospheric. Under these circumstances the molecular mean free path len ... 

Comparing this with equation (A.2.2), it is seen to predict exactly the same dependence of che effusion rate on pressure and temperature. Furthermore, Che ratio of specific heats y depends relatively weakly on che nature of the gas, through its molecularity, so che prediction chat dV/dt 1/M, which follows from equation (A-2.2) and agrees with Graham s results, is not markedly inconsistent with equation (A.2.3) either. 

Effusion separator (or effusion enricher). An interface in which carrier gas is preferentially removed from the gas entering the mass spectrometer by effusive flow (e.g., through a porous tube or through a slit). This flow is usually molecular flow, such that the mean free path is much greater than the largest dimension of a traverse section of the channel. The flow characteristics are determined by collisions of the gas molecules with surfaces flow effects from molecular collisions are insignificant. 

Separator GC/MS interface. An interface in which the effluent from the gas chromatograph is enriched in the ratio of sample to carrier gas. Separator, molecular separator, and enricher are synonymous terms. A separator should generally be defined as an effusion separator, a jet separator, or a membrane separator. 

Fig. 4. Schematic of a high vacuum molecular beam epitaxy (MBE) chamber containing four effusion (Knudsen) cells. Also shown is a high energy electron...

As we have implied, diffusion is a rather complex process so far as molecular motion is concerned. Effusion, the flow of gas molecules at low pressures through tiny pores or pinholes, is easier to analyze using kinetic theory. 

A hydrocarbon of empirical formula C,H, takes 349 s to effuse through a porous plug under the same conditions of temperature and pressure, it took 210. s for the same number of molecules of argon to effuse. What is the molar mass and molecular formula of the hydrocarbon ... 

It took 7.73 min for a given volume of the compound to effuse through a porous plug, but it took only 6.18 min for the same amount of Ar to diffuse at the same temperature and pressure. What is the molecular formula of the compound ... 

Rates of molecular motion are directly proportional to molecular speeds, so Equation predicts that for any gas, rates of effusion and diffusion increase with the square root of the temperature in kelvins. Also, at any particular temperature, effusion and diffusion are faster for molecules with small molar masses. 

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