Molecular valved sources

Figure 13.7. Concept of responsive nanocomposites. Organization of stimuli responsive iigands within a 3-D porous framework imparts new molecular-level functionality, useful for opening and closing a nanoscale valve. Source From Liu et al., 2003a. Reprinted with permission.

A fixed general valve is installed in the source I chamber. H2 (or HD, D2) molecules are collimated by a skimmer and then colhde and react with fluorine atom beam, which is double-skimmer collimated, in scattering chamber. The two molecular beam sources in this experiment will be described below. 

The operation sequence (see Fig. 4) starts with a molecular pulse of 1,000 ps duration which drives the carrier gas flow through the pulsed valve source. After an adequate delay ( 850 ps), a laser pulse hits the solid and vaporizes the sample. To reduce sample consumption, four separate broadband rotational spectra are... 

These types of concepts and ideas are of real importance for demonstrating the use of direct molecular interactions to control the way in which liquids move though microfluidic channels—no conventional valves are needed, and the material can be completely embedded within the manifold, with no need for external connections to circuitry or power sources. 

Among the external processes possibly influencing the rate of overall adsorption, the access of the dif-fusants into the sorption vessel and the dissipation of the adsorption heat deserve special attention. A substantial number of models have been developed to quantify these influences, which are generally referred to as the valve effect [37-39] and the heat effect [2, 40-42], In turn, in Ref. 43 a novel method for uptake measurements has been based on the heat effect during molecular sorption. By IR monitoring of the surface temperature it has become possible to acquire a second, independent source of information about the internal processes within the sample, yielding useful in formation in particular for fast processes. 

Fig. 7 Schematic of an automated direct probe system for molecular weight determination that features an ion trap MS. Samples are dissolved in a suitable solvent and injected via an automated syringe system onto the DEP wire. The probe is injected into the MS via an automated isolation valve system and the temperature is ramped to the programmed temperature. After sample analysis the probe is removed from the source and heated to a high temperature to clean the DEP wire in preparation for the next sample. This type of integrated, open-access MS-based application provides routine, unattended support for medicinal chemistry needs such as reaction monitoring and the optimization of reaction conditions. (Courtesy of Scientific Instrument Services, Ringoes, NJ.)...

Fig. 1.1. Details of the high-frequency iaser evaporation source. Shown are the rotary motor, which drives the planetary gear assembly for turning the target, and the thermalization chamber with exchangeable expansion nozzie. The iaser-produced plasma expands into this thermalization chamber. A heiium gas puise is then introduced by a piezo-driven pulsed valve and synchronized with the iaser puise into the same volume. The metal-gas mixture then expands through the nozzie into the vacuum leading to cluster formation. In contrast to conventional sources, the laser beam is coaxial to the molecular beam axis. The bellow is used to aiign the source along the optical axis of the ion optics...

The breakthrough experiment was carried out by Whitham et al. [39,40] in France. They used a Smalley-type laser vaporization source (Fig. 4) to provide a molecular beam of Ca atoms entrained in He or Ar gas. The second harmonic (532 nm) from a pulsed Nd YAG laser was focused (Fig. 4) on a rotating calcium rod. About 500 jus prior to this, a pulsed valve (left side of Fig. 4) is opened and the plume of vaporized metal is entrained in Ar or He gas. The carrier gas is seeded with a few percent of the oxidant such as H20. The plume of excited- and ground-state metal atoms are carried down a short channel and react with the oxidant. At the end of the channel, the product molecules such as CaOH expand into the vacuum chamber and cool. After a short expansion, the pressure has dropped so low that the molecules are effectively in a collisionless, ultracold (<10K) environment. 

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