Beams supersonic beam

Supersonic beam. Supersonic beam techniques are a well established means for producing intense beams of hyperthermal species with narrow energy distributions. Atomic oxygen may be accelerated to hyperthermal... 

Syage J A, Felker P M and Zewail A H 1984 Picosecond dynamics and photoisomerization of stilbene in supersonic beams. I. Spectra and mode assignments J. Chem. Phys. 81 4685-705... 

The fonnation of clusters in the gas phase involves condensation of the vapour of the constituents, with the exception of the electrospray source [6], where ion-solvent clusters are produced directly from a liquid solution. For rare gas or molecular clusters, supersonic beams are used to initiate cluster fonnation. For nonvolatile materials, the vapours can be produced in one of several ways including laser vaporization, thennal evaporation and sputtering. 

If a particularly parallel beam is required in the chamber into which it is flowing the beam may be skimmed in the region of hydrodynamic flow. A skimmer is a collimator which is specially constructed in order to avoid shockwaves travelling back into the gas and increasing 7). The gas that has been skimmed away may be pumped off in a separate vacuum chamber. Further collimation may be carried out in the region of molecular flow and a so-called supersonic beam results. When a skimmer is not used, a supersonic jet results this may or may not be collimated. 

In a skimmed supersonic jet, the parallel nature of the resulting beam opens up the possibility of observing spectra with sub-Doppler resolution in which the line width due to Doppler broadening (see Section 2.3.4) is reduced. This is achieved by observing the specttum in a direction perpendicular to that of the beam. The molecules in the beam have zero velocity in the direction of observation and the Doppler broadening is reduced substantially. Fluorescence excitation spectra can be obtained with sub-Doppler rotational line widths by directing the laser perpendicular to the beam. The Doppler broadening is not removed completely because both the laser beam and the supersonic beam are not quite parallel. 

Those fixed-angle measurements reported to date have all used either a heated effusive inlet, or heated gas cell for sample admission [55, 56, 61, 62, 65]. Probably the higher sample number densities these sources generate, compared to a supersonic beam source, provides some compensation for the reduced collection efficiency in the fixed-angle measurement. 

Figure 7.2. The uptake of carbon by dissociative adsorption of methane on Ni(lll) follows f rst-order kinetics. The experiment involved dosing the surface with a supersonic beam of molecular methane at the indicated...

Since the demonstration by Schumacher et al ) of the use of alkali metal vapor inclusion into a supersonic beam to produce clusters, there have been a number of attempts to generalize the approach. It has recently been recognized that instead of high temperature ovens, with their concommitant set of complex experimental problems, an intense pulsed laser beam focused on a target could be effectively used to produce metal atoms in the throat of a supersonic expansion valve. ) If these atoms are injected into a high pressure inert gas, such as helium, nucleation to produce clusters occurs. This development has as its most important result that clusters of virtually any material now can be produced and studied with relative ease. 

Detection limits in the lOOfg range can be obtained with a tuneable UV laser working at a wavelength of maximum absorption for the compounds of interest. Continuous supersonic beams require high gas loads and combination with a pulsed ionisation technique (e.g. REMPI) is unfavourable in terms of sensitivity. Pulsed valves are a better approach for a GC-UV-MS interface [1021]. 

Fig. 4. Electron-impact efficiency curves at m/e = 32 and rri/e = 16 for a supersonic beam of O2. Arrows indicate the literature values72 of the ionization energy of O2 and of the appearance energy of 0+.

The scope of this review focuses on photodissociation dynamics of free radicals in supersonic beam. The review concentrates on the new studies since the last review of this subject by Whitehead in 1996.1 Due to the recent advances in high-intensity lasers and product detection schemes, as... 

Figure 1 is a schematic of the laser vaporization source. This diagram depicts a pulsed valve on the left which supplies high pressure helium flow directly towards the right. Several workers have also chosen to use continuous helium f ows(2,6,9). In general these sources are modifications of conventional supersonic beam sources. 

A technique which is not a laser method but which is most useful when combined with laser spectroscopy (LA/LIF) is that of supersonic molecular beams (27). If a molecule can be coaxed into the gas phase, it can be expanded through a supersonic nozzle at fairly high flux into a supersonic beam. The apparatus for this is fairly simple, in molecular beam terms. The result of the supersonic expansion is to cool the molecules rotationally to a few degrees Kelvin and vibrationally to a few tens of degrees, eliminating almost all thermal population of vibrational and rotational states and enormously simplifying the LA/LIF spectra that are observed. It is then possible, even for complex molecules, to make reliable vibronic assignments and infer structural parameters of the unperturbed molecule therefrom. Molecules as complex as metal phthalocyanines have been examined by this technique. 

No doubt this will change soon as fundamental understanding extends to more complex molecules. For example, the supersonic beam techniques described earlier show promise in elucidating the vibronic states of relatively complex molecules, if they have adequate volatility. 

Nozzle Beams, Supersonic (Anderson, Andres, Fenn). Nuclear Magnetic Relaxation Methods for the Study of 10 275... 

A. Latini, D. Toja, A. Giardini Guidoni, S. Piccirillo, and M. Speranza, Energetics of molecular complexes in a supersonic beam A novel spectroscopic tool for enantiomeric discrimination. Angew. Chem. Int. Ed. 38, 815 817 (1999). 

Page, R. H., Shen, Y. R., and Lee, Y. T. (1988), Local Modes of Benzene and Benzene Dimer, Studied by Infrared-Ultraviolet Double Resonance in a Supersonic Beam, J. Chem. Phys. 88, 4621, 5362. 

Neutral clusters from supersonic beam 157 Spectroscopy of neutral clusters 158 Sources of ionic clusters 167 Mass spectrometry of ionic clusters 170... 

Fig. 3 Relative dipole-bound anion formation rates in RET collisions between Rydberg Xe(nf) atoms with (a) adenine (circles) or imidazole (squares) molecules and (b) adenine-imidazole complex produced in a supersonic beam. Experimental data are fitted to curvecrossing model calculations which lead to the experimental determination of EAdS values, equal to 11 meV for adenine, 23 meV for imidazole and 54 meV for adenine-imidazole complex (reproduced by permission of the American Chemical Society).

Fig. 14 Relative dipole bound anion formation rates in RET collisions between Rydberg Xe(nf) atoms and a supersonic beam of (R)-l-phenylethanol (E/ ) with 2-pyrrolidinmethanols (PRand P5).

Tembreull R, Lubman DM. 1984. Use of resonant two-photon ionization with supersonic beam mass spectrometry in the discrimination of cresol isomers. Anal Chem 56(11) 1962-1967. 

The combined pump and probe beams are focused onto a supersonic beam of reactant in helium within a vacuum chamber containing a time-of-flight mass spectrometer. The pump pulse promotes the reactant to some excited state the probe... 

Figure 6.12 Experimental two-color setup featuring an IR beamline, to generate intense shaped IR pump pulses, and a VIS probe beamline, to provide time-delayed probe pulses of a different color. Both beams are focused collinearly into a supersonic beam to interact with isolated K atoms and molecules. Photoelectrons released during the interaction are measured by an energy-calibrated TOE spectrometer. The following abbreviations are used SLM, spatial light modulator DL, delay line ND, continuous neutral density filter L, lens S, stretcher T, telescope DM, dichroic mirror MCP, multichannel plate detector.

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