Scattering velocity distribution

J. Lorenzen and L.M. Raff. A Comparison of Detailed Lattice Model Gas-Solid Theory with Molecular Beam Data Scattered Velocity Distributions for an Ar/W System. J. Chem. Phys. lA. i929 (1981). 

Figure 7 TOF spectrum of trimethylgallium (TMG) from the (2 X 4)-reconstructed QaAs(IOO) surface at 638 K when a pulsed TMG beam is supplied to the surface. The spectrum is well reproduced by convolution of the incident and scattered velocity distributions as well as a surface residence time of 0.9 ns. (Reproduced with permission from Sasaki M and Yoshida S (1996) Scattering of pulsed trimethylgallium beam from GaAs(IOO), -(110), and -(111) B surfaces. Surface Science 356 233-246 Elsevier.)...

In TOF-SARS [9], a low-keV, monoenergetic, mass-selected, pulsed noble gas ion beam is focused onto a sample surface. The velocity distributions of scattered and recoiled particles are measured by standard TOF methods. A chaimel electron multiplier is used to detect fast (>800 eV) neutrals and ions. This type of detector has a small acceptance solid angle. A fixed angle is used between the pulsed ion beam and detector directions with respect to the sample as shown in figure Bl.23.4. The sample has to be rotated to measure ion scattering... 

A molecular beam scattering experiment usually involves the detection of low signal levels. Thus, one of the most important considerations is whether a sufficient flux of product molecules can be generated to allow a precise measurement of the angular and velocity distributions. The rate of fonnation of product molecules, dAVdt, can be expressed as... 

In a crossed-beam experiment the angular and velocity distributions are measured in the laboratory coordinate system, while scattering events are most conveniently described in a reference frame moving with the velocity of the centre-of-mass of the system. It is thus necessary to transfonn the measured velocity flux contour maps into the center-of-mass coordmate (CM) system [13]. Figure B2.3.2 illustrates the reagent and product velocities in the laboratory and CM coordinate systems. The CM coordinate system is travelling at the velocity c of the centre of mass... 

C3.3.4 DEDUCING ENERGY TRANSFER MECHANISMS FROM POPULATION AND VELOCITY DISTRIBUTIONS OF THE SCATTERED BATH MOLECULES ROTATIONAL STATE POPULATION DISTRIBUTIONS FOR VIBRATIONAL EXCITATION OF THE BATH... 

Single-component PDA equipment is similar to LDA, but two detectors (not one) are installed with different detection angles. By means of simultaneous processing of signals supplied by the two detectors, information on the velocity and on the size of the scattering objects can be acquired. Therefore, velocity distribution, size distribution, and number density (local concentration)... 

The energetics of the Eley-Rideal reaction (A E —230 kJ mol-1) are well established.42 Here, the highly exoergic reaction forming gas-phase HC1 was probed by time-of-flight velocity measurements,39,41 scattering angular distributions,39,41 and state-selective laser spectroscopy.39-41... 

The quantum-mechanical ionization cross section is derived using one of several approximations—for example, the Born, Ochkur, two-state, or semi-classical approximations—and numerical computations (Mott and Massey, 1965). In some cases, a binary encounter approximation proves useful, which means that scattering between the incident particle and individual electrons is considered classically, followed by averaging over the quantum-mechanical velocity distribution of the electrons in the atom (Gryzinski, 1965a-c). However, Born s approximation is the most widely used one. This is discussed in the following paragraphs. 

Methods for analysis of the particle size distribution in the aerosol cloud include techniques such as time of flight measurement (TOE), inertial impaction and laser diffraction. Dynamic light scattering (photon correlation spectroscopy) is confined to particles (in suspension) in the submicron range. In addition to the size distribution, the particle velocity distribution can be measured with the Phase Doppler technique. 

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