Collision system

Reactive scattering or a chemical reaction is characterized by a rearrangement of the component particles within the collision system, thereby resulting in a change of the physical and chemical identity of the original collision reactants A + B into different collision products C + D. Total mass is conserved. The reaction is exothemiic when rel(CD) > (AB) and is endothermic when rel(CD) < (AB). A threshold energy is required for the endothemiic reaction. 

The wavefiinction for the complete A-B collision system satisfies the Sclirodinger equation... 

The total Hamiltonian of the collision system can be most generally written as the sum of three terms the kinetic energy of the relative motion, the interaction potential between the colliding particles, and the asymptotic Hamiltonian describing the colliding particles at infinite separation. We make the following approximations ... 

Figure 8.1 Schematic structure of the Hamiltonian matrix for a collision system in an external field expressed in the total angular momentum representation.

Second, most of the articles cited and the calculations presented are for collisions of diatomic molecules with atoms. The effects of external fields have been studied only for three molecule-molecule collision systems O2-O2 in a magnetic field, NH-NH in a magnetic field, and OH-OH in an electric field. In each case, the calculations are based on significant simplifications of the interaction potential operator. Most of the NH-NH calculations and the O2-O2 studies assume that the collision dynamics occurs on the maximal spin adiabatic potential energy surface of the two-molecule complex. There is only one study that considers the dynamics of NH-NH collisions in a magnetic field with account of transitions to lower spin surfaces [48]. 

The coherent fs time-resolved CARS method is highly sensitive for the investigation of collision induced (or pressure dependent) changes in optical line shapes especially when line mixing occurs and frequency resolved measurements come to their limits [7]. The fs-CARS spectroscopy is applied to various collision systems (N2-N2, N2-rare gas, C2H2-C2H2, CO-CO)... 

Fig. 2. Fs CARS transients of various collision systems and AECS model fit.

Fig. 3. Numerical calculation of zc for the N2-N2 collision system from the interaction potential. The table shows fitted values of rr for various collision systems from experimental data.

The initial kinetic energy may be relatively well defined. For quenching by N2, which is typical for the heavier molecules, we have the initial kinetic energy of the collision system defined to in=150 meV 100 meV (FWHM) at To=300°K and (125 60) meV at ro=80°K, which is already better than that for thermal conditions and may be improved drastically by also using a supersonic molecular beam. 

H is the reduced mass of the collision system, and R, is determined as the outermost root of u,( ) = 0. In expression (II.8) contributions from on the way in and on the way out are contained. Integration with respect to R leads to the transition probability along the whole trajectory with angular momentum /. We obtain the simple result... 

Figure 28. Electron spectrum for collision system He -Kr at various collision energies. Broad distribution at low electron energies is a result of Penning ionization, and narrow peaks arise from atomic autoionization of krypton following excitation transfer from He to Kr.77...

Figure 35. Electron spectrum for thermal collision system Ar(3P2 0)-H. Dashed line at low energy indicates estimated transmission corrected intensity.99,100...

Fig. 22 shows the results of photometry of plates similar to that illustrated in Fig. 21. The relative intensities of suitable transitions were determined from the asymptotic limit at long time delays when the system attains equilibrium. (These resemble, but are not identical to, the relative/ values because of the usual instrumental effects which depend on line width.) The time variation of the relative concentrations is shown in Fig. 23 the upper four levels attain Boltzmann equilibrium amongst themselves after 100 /isec, to form a coupled (by collision) system overpopulated with respect to the 5DA state. The equilibration of the upper four levels causes the initial rise (Fig. 22) in the population of Fe(a5D3). Thus relaxation amongst the sub-levels is formally similar to vibrational relaxation in most polyatomic molecules, in which excitation to the first vibrational level is the rate determining step. In both cases, this result is due to the translational overlap term, for example, in the simple form of equation (14) of Section 3.

Figure 1. Collision system and coordinate frame T and P represent respectively target and projectile centers the impact velocity n is parallel to the z-axis and the impact parameter b to the x-axis. r and i are the respective positions of the electron and the projectile relatively to the target.

We have presented results which extend and confirm Janev el al. recommanded data for the C6+- H(l.s) collision system. The problems raised by the choice of the intemuclear trajectory in semi-classical methods were shortly discussed. A more detailed study regarding those questions is in progress [21],... 

SINGLE AND DOUBLE ELECTRON CAPTURE IN BORON COLLISION SYSTEMS... 

Single and double electron capture in boron collision systems 133... 

An electron-atom or electron-molecule collision system consists of particles that never annihilate and that interact each other only via Coulomb forces. 

If the collision system can separate asymptotically into a pair of charged particles of opposite signs, the attractive Coulomb tail of the interaction between them supports an infinite number of bound Rydberg states in each closed channel (with a threshold energy Eth). Its coupling with open channels, if any, normally turns these bound states into an infinite series of quasi-bound... 

The HSCC equations have been solved for various Coulomb three-body processes, such as photoionization and photodetachment of two-electron systems and positronium negative ions [51, 105-111], electron or positron collisions [52, 112-115], ion-atom collisions [116-119], and muon-involving collision systems [103, 114, 120-125]. Figures 4.6, 4.7, 4.8, 4.9, and 4.10 are all due to HSCC calculations. Figure 4.12 illustrates the good agreement between the results of HSCC calculations [51] and the high-resolution photoionization experiment on helium [126]. See Ref. [127] for further detailed account of the comparison between the theory and experiment on QBSs of helium up to the threshold of He+(n = 9). 

A procedure in this time-independent approach that corresponds to following the time evolution of the collision system would be to study the annihilation function x P p) defined in terms of the hyperspherical coordinates by... 

Collision System Lattice Type Coverage (ML) HD Formation H2 or D2 Formation Sticking Bulk H or D Reflection... 

We are discussing our manner to calculate the total energy for small molecules within the DV-Xa approximation by using only the monopol part of the potential in the solution of the Poisson equation. A discussion of the relativistic effects, including our results for heavy diatomic molecules, is followed by remarks on the choice of the exchange-correlation potential together with our results of calculations on molecules for the element 106 and their chemical interpretation. We conclude with results on very heavy correlation diagrams for collision systems with a united Z above 110. 

When our present group became interested in quasi-molecules, which are generated in atomic collision systems, we started to use the relativistic DV Xa-method. With the help of Arne Rosen we were the first to calculate correlation diagrams of relatively heavy systems. ... 

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