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Manuscript Title: Rate constants for vibrational transitions in diatom-diatom collisions.
Authors: G.D. Billing
Program title: DIDIEX
Catalogue identifier: AATY_v1_0
Distribution format: gz
Journal reference: Comput. Phys. Commun. 44(1987)121
Programming language: Fortran.
Computer: UNIVAC 1110/92.
RAM: 72K words
Word size: 36
Keywords: Molecular physics, Elastic, Rotational energy Transfer, Diatom-diatom, Collision, Semiclassical scattering, Theory.
Classification: 16.7.

Revision history:
Type Tit le Reference
correction 000ACORRECTION 14/11/88 See below

Nature of problem:
The problem considered is the transfer of vibrational energy in the collision of two diatomic molecules. The translational and rotational motion of the two diatomic molecules are treated classically; the vibrational motion is quantized.

Solution method:
A set of coupled first order differential equations for the classical trajectories and the quantum amplitudes are integrated using an Adams variable-order, variable step size method. Monte Carlo averaging over initial variables is carried out so as to obtain the average cross sections which should be used in the program RATECONS (catalogue number: ACFW) in order to calculate rate constants as a function of temperature.

Unusual features:
The program uses four subroutines from the NAG-library. These may, however, easily be substituted by other library routines (see long write-up). Furthermore two user-supplied routines are called.

Running time:
From a few seconds to several minutes per trajectory. Cross sections converge to within 10-20% with about 50-200 trajectories at a given energy. In order to compute rate constants in a temperature range 50- 4000K one typically needs cross sections at 5-10 energies.

CORRECTION SUMMARY
Manuscript Title: Rate constants for vibrational transitions in diatom-diatom collisions. (C.P.C. 44(1987)121).
Authors: G.D. Billing
Program title: 000ACORRECTION 14/11/88
Catalogue identifier: AATY_v1_0
Distribution format: gz
Journal reference: Comput. Phys. Commun. 52(1989)443
Classification: 16.7.