Collision processes

Muschlitz E E 1957 Formation of negative ions in gases by secondary collision processes J. Appi. Rhys. 28 1414-18... 

As with any collision process, to understand the dynamics of collisions we need an appreciation of the relevant forces and masses. Far from the surface, the incoming atom or molecule will experience tire van der Waals attraction of the fonn... 

All the theory developed up to this point has been limited in the sense that translational motion (the continuum degree of freedom) has been restricted to one dimension. In this section we discuss the generalization of this to three dimensions for collision processes where space is isotropic (i.e., collisions in homogeneous phases, such as in a... 

Steinfeld J I, Ruttenberg P, Millot G, Fanjoux G and Lavorel B 1991 Scaling laws for inelastic collision processes in diatomic molecules J. Phys. Chem. 95 9638—47... 

Table C2.13.1 Collision processes of electrons and heavy particles in non-thennal plasmas. The asterisk denotes short-lived excited particles, the superscript m denotes long-lived metastable excited atoms or molecules.

The probability for a particular electron collision process to occur is expressed in tenns of the corresponding electron-impact cross section n which is a function of the energy of the colliding electron. All inelastic electron collision processes have a minimum energy (tlireshold) below which the process cannot occur for reasons of energy conservation. In plasmas, the electrons are not mono-energetic, but have an energy or velocity distribution,/(v). In those cases, it is often convenient to define a rate coefficient /cfor each two-body collision process ... 

In stark contrast to tire results shown in figure C3.3.5 are data obtained for collision processes tliat lead to no... 

The END trajectories for the simultaneous dynamics of classical nuclei and quantum electrons will yield deflection functions. For collision processes with nonspherical targets and projectiles, one obtains one deflection function per orientation, which in turn yields the semiclassical phase shift and thus the scattering amplitude and the semiclassical differential cross-section... 

The inelastic collision process is characterized by an inelastic mean free path, which is the distance traveled after which only 1/e of the Auger electrons maintain their initial energy. This is very important because only the electrons that escape the sample with their characteristic Auger energy are usefrd in identifying the atoms in... 

Gelbart (1974) has reviewed a number of theories of the origins of the depolarized spectrum. One of the simplest models is the isolated binary collision (IBC) model of McTague and Bimbaum (1968). All effects due to the interaction of three or more particles are ignored, and the scattering is due only to diatomic collision processes. In the case that the interacting particles A and B are atoms or highly symmetrical molecules then there are only two unique components of the pair polarizability tensor, and attention focuses on the anisotropy and the incremental mean pair polarizability... 

If a particle A must know B s total information content before colliding, the collision process must be delayed until A has full access to that information. However, such a delay is consistent neither with classical nor quantum mechanics, Minsky instead suggests that the collision proceeds immediately, but with the particles both working with less than all the information that is classically required i.e, the incoming particles momenta are estimated. Outgoing momenta are determined via conventional classical rules, but, because of the estimation errors, each scattered particle leaves behind a receipt recording how much momentum was really taken away in the process. Receipts not only mark prospective event-locations at which future collisions might take place, but harbor information that can be used to estimate new real momenta. 

The differences between x-ray and electron excitation must obviously stem from differences in the interaction of x-rays (1.11) and of electrons (1.4) with matter. Electrons are retarded rather quickly when they strike a sample, and they lose much of their energy in classical collision processes (4.1). Because electrons transfer their energy so rapidly, the critical thickness (Equation 6-8) for electron excitation is very much less than we saw it to be for x-ray excitation a.calculation based on experiments on a variety of materials53 gives 1CT3 cm (105 A) as a good value for the depth to which 50-kv electrons penetrate aluminum, and bears out the previous statement. Because the energy of every electron decreases as it penetrates, the x-ray excited by any electron will be of... 

Discussion of the Equation.—The Boltzmann equation describes the manner in which the distribution function for a system of particles, /x = /(r,vx,f), varies in terms of its independent variables r, the position of observation vx, the velocity of the particles considered and the time, t. The variation of the distribution function due to the external forces acting on the particles and the action of collisions are both considered. In the integral expression on the right of Eq. (1-39), the Eqs. (1-21) are used to express the velocities after collision in terms of the velocities before collision the dynamics of the collision process are taken into account in the expression for x(6,e), from Eqs. (1-11) and (1-12), which enters into the k of Eqs. (1-21). Alternatively, as will be shown to be useful later, the velocities before and after collision may be expressed, by Eq. (1-20), in terms of G,g, and g the dynamics of the collision comes into the relation between g and g of Eq. (1-19). 

From a mathematical perspective either of the two cases (correlated or non-correlated) considerably simplifies the situation [26]. Thus, it is not surprising that all non-adiabatic theories of rotational and orientational relaxation in gases are subdivided into two classes according to the type of collisions. Sack s model A [26], referred to as Langevin model in subsequent papers, falls into the first class (correlated or weak collisions process) [29, 30, 12]. The second class includes Gordon s extended diffusion model [8], [22] and Sack s model B [26], later considered as a non-correlated or strong collision process [29, 31, 32],... 

The collision process can be captured by a high speed video camera as shown in Fig. 6 [14]. The slurry is about 50 mm apart away from the solid surface at 0 s (Fig. 6(a)), and reaches the surface at 0.018 s (Fig. 6(b)). Then the slurry reflects at an angle as same as the incidence angle (Fig. 6(c)). As time goes, the reflected liquid beam is divided into two beams, one is in the reflected direction and another is parallel to the solid surface as shown in Fig. 6(d). When time reaches 0.068 s, most of the reflected slurry moves along the solid surface. 

Figure 18 [28] shows the variation of the particle speed and the potential energy of the silicon wafer in the collision process. The dashed line means the speed of the particle in the vertical direction and the black one indicates the variation of potential energy of the silicon disk. When the particle penetrates into the wafer surface, its vertical speed becomes lower and lower. Once the particle reaches the deepest position, the speed of the particle becomes zero and the potential energy of the silicon wafer increases to the highest one, and... 

Fig. 18—Potential energy of Si disk and particle speed in vertical direction during the collision process with an incident angle of 45° at an incident speed of 2200 m/s.

An important point is that these advances have been complemented by the concomitant development of innovative pulse-characterisation procedures such that all the features of femtosecond optical pulses - their energy, shape, duration and phase - can be subject to quantitative in situ scrutiny during the course of experiments. Taken together, these resources enable femtosecond lasers to be applied to a whole range of ultrafast processes, from the various stages of plasma formation and nuclear fusion, through molecular fragmentation and collision processes to the crucial, individual events of photosynthesis. 

J. Cooper and R. N. Zare, Photoelectron angular distributions. In Sydney Geltman, KalayanaT. Mahanthappa, and Wesley Emil Brittin (ed.). Lectures in theoretical physics Vol. 11c. Atomic collision processes, Gordon and Breach, New York, 1969, pp. 317—337. 

In general, the substrate temperature will remain unchanged, while pressure, power, and gas flow rates have to be adjusted so that the plasma chemistry is not affected significantly. Grill [117] conceptualizes plasma processing as two consecutive processes the formation of reactive species, and the mass transport of these species to surfaces to be processed. If the dissociation of precursor molecules can be described by a single electron collision process, the electron impact reaction rates depend only on the ratio of electric field to pressure, E/p, because the electron temperature is determined mainly by this ratio. 

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