Crossed beam machine

Fig. 2. Schematic of the rotatable sources, crossed-beam machine. 

Figure 3. Illustration of the cross-beam machine. N is the nozzle source for the molecular beam, C is the buffer chamber with a beam chopper (not shown), H is the hexapole electric field quantum state selector, U are the homogeneous electric field plates, Q is an on-axis quadrupole mass filter, O is the fast atom beam source, and Q and C,8o are channeltrons.

Reaction 16 was first laser induced by Happer and co-workers in a cell experiment under a multi-collision regime, which allowed, spectacularly, the product CsH to condense as powder, the so-called laser snow [144]. The dynamic picture of this reaction has emerged from a series of studies by Vetter and co-workers using a crossed-beam machine where cesium was excited to both the levels 6d [145] and 7p P [146-150]. The most interesting result concerns the reaction dynamics of cesium in the (7p Pi/2) level, which was interpreted after ah initio potential energy surface, semi-classical and quantal dynamics calculations [151 153]. The reaction of cesium in the 8p P and 9p P Rydberg levels with hydrogen molecules has also been studied [154]. 

In a typical CMB experiment, beams of atoms and molecules with narrow angular and velocity spread are crossed in a vacuum chamber and the angular and time-of-flight (TOF) distributions of the products are recorded after well defined collisional events take place. The detector is an electron-impact ionizer followed by a quadrupole mass spectrometer (QMS) filter the whole detector unit can be rotated in the collision plane around the axis passing through the collision center (Figure 14.1). The crossed beam machine used in the present experiments has been described in detail elsewhere [67, 79,80]. Briefly, it consists of two source chambers (10 mbar), a stainless-steel scattering chamber (10 mbar), and a rotatable, differentially pumped quadrupole mass spectrometric detector ( <8 X 10" mbar). 

In Fig. 2 a schematic of a crossed-beam machine used by Herman s group in Prague is shown.15 It will be noted that this spectromer uses magnetic... 

Initially the molybdenum fluxes in [55] measured via atomic Mo-lines (379.8 nm, 386.4 nm and 390.3 nm) led to unreasonably high flux values. This was the case because for the calculation of the respective excitation rates the formula of van Regemorter was used [56], as these lines are optically coupled to the ground state (resonance lines). Therefore, experiments were performed to measure the excitation and ionization rates directly both in a linear plasma machine [57] and in a crossed beam experiment with a thermal molybdenum emitter [58], The results can be seen in Fig. 6.17 and show that the experimental values for excitation are about a factor of 5 larger than those from the van Regemorter formula, which leads to a reduction of the flux by the same order according to the smaller S/XB. More refined R-Matrix calculations have later confirmed the same factor and are included in Fig. 6.3. 

FIGURE 11.1 Top view of the crossed molecular beams machine. Shown are the main chamber, the primary (laser ablation configuration) and secondary source chambers, and the rotatable differentially pumped mass spectrometer detector. 

Resist films of approximately 0.5ym thickness were spun on silicon wafers and cross inked by baking either in an oven or on a hotplate. Incremental exposures were made by a JEOL JBX6A2 electron beam machine at 20 keV. The UV flood exposures were carried out under nitrogen using a 185nm UV lamp. UV dosimetry was carried out on the basis of exposure time which had previously been correlated with the equivalent electron beam exposure by measuring dissolution rates. 

Crossed molecular beam machines count among the experimental arrangements which allowed a significant breakthrough in reaction dynamics. A recent review by Casavecchia et al. shows how improvements in the crossed molecular beam technique made possible recent progresses in the understanding of gas-phase reaction dynamics [14]. 

Fig. 2.7 Photograph of HRTOF crossed molecular beam machine...

The first such crossed-beam apparatus was described by Turner et The machine was designed to measure angular distributions and differential cross sections, but not energy spectra. Since it has not been extensively used, it will not be described further here. 

FIGURE 14.21 Schematic of the crossed-beam scattering machine. Each decelerator has a modular design and consists of a total of 300 electric field stages. As shown in the inset, the decelerators are designed such that their exits come very close to the collision zone, while simultaneously providing excellent optical access for detection of the scattered products (design Henrik Haak). 

For a more detailed characterization of the IRP-method we will briefly discuss apparatus and experimental technique recently used to measure m- and j-dependent cross sections for the reaction K + HF(v=l,j,m) -> KF + H [7,9], Figure 1 shows a schematic drawing of the crossed molecular beams machine together with the optical set up employed to prepare HF via IRP. 

A home-designed device was used to align the fibre with the axis of a Hounsfield tensile testing machine. The upper part of the card-board was clamped on a 5N load cell, which was fixed on the cross-beam of the tensile testing machine. The pull-out speed was 1 mm/min. Force-displacement curve was recorded on a computer. The interfacial shear strength, t, was calculated using Eq. 3. 

Henglein (23) has constructed a machine for studying stripping reactions which does not fall into any of the above categories. It consists of an ion gun followed by a flight tube which also serves as a reaction chamber. A velocity selector scans the ions which have suffered little or no change in direction, and energy analysis of the secondary ion beam is used to deduce cross-sections and reaction mechanisms in chosen simple cases. 

ICT machines produced recently have energy ratings from 0.3 to 3.0 MeV and beam power capabilities up to 100 kW. Nearly 180 of these machines, the majority of them rated for less than 1 MeV, have been installed as of the early 1990s. They are used mainly for cross-linking of heat-shrinkable film, plastic tubing, and electric wire. ... 

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