Beam sources nozzle

Valentin J J, Coggiola M J and Lee Y T 1977 Supersonic atomic and molecular halogen nozzle beam source Rev. Sc/. Instrum 48 58-63... 

The spectrometer is fitted with a skimmed c.w. supersonic molecular beam source. Many chiral species of interest are of low volatility, so a heated nozzle-reservoir assembly is used to generate, in a small chamber behind a 70-pm pinhole, a sample vapor pressure that is then seeded in a He carrier gas as it expands through the nozzle [103], Further details of this apparatus are given elsewhere [36, 102, 104],... 

Figure 3.9. Transient C02 formation rates on Pd30 (a) and Pd8 (b) mass-selected clusters deposited on a MgO(lOO) film at different reaction temperatures [74]. In these experiments CO was dosed from the gas background while NO was dosed via a pulsed nozzle molecular beam source. The turnover frequencies (TOFs) calculated from the experiments displayed in (a) and (b) are displayed in the last panel (c). C02 formation starts at lower temperatures but reaches lower maximum rates on the larger cluster. (Figure provided by Professor Heiz and reproduced with permission from Elsevier, Copyright 2005).

Fig. 2. Schematic diagram of a high resolution He time-of-flight spectrometer. N-nozzle beam source, SI, 2-skimmers, Al-5 - apertures, T - sample, G - gas doser, CMA - Auger Spectrometer, IG - ion gun, L - LEED, C -magnetically suspended pseudorandom chopper, QMA-detector, quadrupole mass analyzer with channeltron.

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.

The experimental setup used by our group is shown in Figure 7-1. This apparatus consists of a molecular beam source coupled to a chamber housing the quadrupole mass spectrometer. The continuous beam source consists of a Campargue-type nozzle, an expansion chamber, and a collimation chamber. The nozzle assembly itself is mounted on a micrometer and is fitted with a gas handling line which... 

Using a seeded nozzle beam source of N02 rather than a thermal beam, it was concluded [260] that the energy disposal is insensitive to reagent rotational excitation, but that there might be a slight increase in rotational excitation of the OH product as the reagent translational energy is increased. 

Two particularly interesting chemiluminescent reactions have been discovered using beams of alkali dimer molecules (M2). These species are formed in high yield in an alkali metal nozzle beam source and they can be separated from the remaining atoms by means of an inhomogeneous magnetic field. This technique has made it possible to study reactions of these diatomic species by molecular beam methods for the first time [364] and as a result it has been demonstrated conclusively that reactions of the type... 

Static gas targets such as those used by Wagenaar and de Heer (1985) are usually unsuitable for differential cross-section measurements. These days scattering experiments are carried out in a crossed-beam arrangement. A large variety of beam sources are used. These range from effusion from simple orifices or capillary arrays to supersonic nozzles, from ovens... 

Anderson JB, Fenn JB (1965) Velocity distributions in molecular beams from nozzle sources. Phys Fluids 8 780... 

The substitution reactionsof fluorine atoms with unsaturated hydrocarbons have been investigated in a comprehensive range of experiments.153-159. A velocity selected beam of F atoms, formed by thermal dissociation of F2 in a nickel oven, is intersected by a hydrocarbon beam from a supersonic nozzle beam source. Angular153 and velocity154 distributions of C2H3F product were measured for the displacement of a hydrogen atom from ethylene... 

Figure 9. View of the essential parts of the crossed beam apparatus using short-lived radioactive labeling and detection (23) Ay radioactive beam source By scrubber-furnace C, LN -cooled collimator D, shut-off plug Ey nozzle beam furnace and cryopump F, gate valve G, hodoscope H, LN -coohd beam trap 7, calibrated beam monitor /, silicon surface barrier detectors K, halogen crossed beam L, radioactive beam M, rotary feed-through used to close the source stopcock.

Figure 21.1 Comparison of molecular and hydrodynamic beam sources. M is the flow Mach number. Top angular distribution for a thermal oven M = 0), a nozzle (M = 10), and a channel beam (CB). Bottom velocity distribution for a thermal oven and a nozzle beam the curves are normalized to the same maximum intensity. Reproduced from Toennies, i n Physicat Chemistry, An Advanced Treatise, VI-A, 1974, with permission of Elsevier...

The details of the crossed-beam apparatus used in our experiment can be found in many earlier publications [17,18]. Briefly, the alkali dimer source consisted of a resistively heated molybdenum oven and nozzle assembly, with the temperatures of the nozzle and the oven being controlled independently by different heating elements. Sodium vapour carried by an inert gas, which was either He or Ne, expanded out of the 0.2 mm diameter nozzle to form a supersonic beam of Na/Na2/inert gas mixture. The Na2 concentration was about 5% molar fraction of the total sodium in the beam when He was used as carrier gas. The beam quality dropped severely when we seeded Na2 in Ne so the dimer intensity became much weaker. No substantial amount of trimers or larger clusters was detected under our experimental conditions. The Na2 beam was crossed at 90 by a neat oxygen supersonic beam in the main collision chamber under single collision conditions. The O2 source nozzle was heated to 473 K to prevent cluster formation. Both sources were doubly differentially pumped. The beams were skimmed and collimated to 2 FWHM in the collision chamber. Under these conditions, the collision energies for the reaction could be varied from 8 kcal/mol to 23 kcal/mol. 

Generation of the Molecular/Cluster Beam. In the first chamber the molecules and clusters are produced in a seeded supersonic nozzle source. It is perhaps the most intense molecular/cluster beam source available. In this source, alkali metal is vaporized in a hot oven as sketched in Fig. 2.19. The alkali... 

J.B. Anderson and J.B. Fenn, Velocity Distributions in Molecular Beams from Nozzle Sources , Phys. Fluids 8, 780 (1965). 

---