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Manuscript Title: Trajectory calculations for the reaction K+HBr -> KBr+H in the eV- region.
Authors: A. van der Meulen
Program title: CLASSICAL TRAJECTORIES 324
Catalogue identifier: AAGI_v1_0
Distribution format: gz
Journal reference: Comput. Phys. Commun. 3(1972)42
Programming language: Algol.
Computer: NV PHILIPS E1-X8.
Operating system: MILLI MCALL.
RAM: 4K words
Word size: 54
Keywords: Atomic physics, Molecular physics, Chemical reaction, Three-dimensional, Classical, Trajectory, Stepsize control, Array elements, Runge-kutta-zonneveld, Second order Differential equations, Potential energy, Charge transfer.
Classification: 16.8.

Nature of problem:
A series of three-dimensional classical kinematic computer trajectory calculations have been made on the exothermic exchange reaction K+HBR - KBr+H, deltaH=-0.206eV. The total reaction cross section for the formation of KBR, as well as the angular distribution of non-reactive scattered K was obtained as a function of initial relative kinetic energy, which was varied between 0.03 and 30eV.

Solution method:
By means of a suitable canonical transformation the 18 equations of motion could be reduced to a system of 6 linear second order coupled differential equations. The integration of this system is performed by means of a specially adapted version of the Runge-Kutta-Zonneveld RK 3n-procedure, with variable stepsize.

Running time:
The evaluation of one complete trajectory takes about 10 s, if the following conditions are satisfied: (i) conservation of energy better than 0.1%; (ii) initial distance between K and the centre of mass of HBr equals 8 Angstrom; (iii) the integration is terminated if at least 2 of the 3 interatomic distances H-Br, K-Br and K-H exceeds 5, 8 and 8.5 Angstrom respectively. Restrictions: The program can easily be modified to accept potential energy functions of any analytic form, rather than the L.E.P.S. expression used in this work.