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Manuscript Title: EROTVIB: a general program to calculate rotationally and/or vibrationally elastic and inelastic cross sections for electron (positron) scattering by spherical, symmetric and asymmetric top molecules.
Authors: A. Jain, D.G. Thompson
Program title: EROTVIB
Catalogue identifier: AAJM_v1_0
Distribution format: gz
Journal reference: Comput. Phys. Commun. 32(1984)367
Programming language: Fortran.
Computer: CYBER-170/750.
Operating system: NOS 1.4.
RAM: 64K words
Word size: 60
Keywords: Spherical top, Symmetric top, Asymmetric top, Point group, Excitation vibrational, Rotational excitation, Scattering elastic, Adiabatic-nuclei Rotation (vibration) Approximations, K-matrix, T-matrix, Body-fixed frame, Closure formula, Total, Differential and Moment transfer Cross sections, Scattering, Electron, Molecule.
Classification: 16.5.

Subprograms used:
Cat Id Title Reference
ACFD_v1_0 ASYMTOP CPC 30(1983)301

Nature of problem:
This program calculates cross sections (total, differential and momentum transfer) for rotationally and/or vibrationally elastic and inelastic scattering of low energy electron (positron) impact by polyatomic molecules. It requires the body-fixed (BF) frame K-matrices for each symmetry (and at each geometry in case of vibrational excitation) as the input. For a polar molecule, the program has the provision to use the closure formula of Crawford and Dalgarno in order to obtain converged cross sections.

Solution method:
The BF frame scattering amplitude is first converted into space-fixed (SF) frame and then the Chase formula, in the adiabatic-nuclei-rotation (vibration) approximation, is employed to derive expressions for rotationally and/or vibrationally elastic and/or inelastic cross sections.

Restrictions:
The program is designed to accept K-matrices only up to the maximum dimension of 22*22. This, in the context of present molecules, means that up to lmax=7 partial waves can be included in the calculation [ in this case, in eq. (1) LBIG=14]. At the same time, the maximum value of the final rotational quantum number (JF(I)) can be only up to 5. However, for JF(I)>5 and lmax >7, the program can easily be modified by changing dimensions of various arrays (described in the code).

Running time:
For the present test case of e-H2O scattering the determination of AL coefficients for LBIG=7 [eq. (1)] takes only 0.2 s. In this calculation, the time to evaluate asymmetric top eigenfunctions is not included; however, this should again be less than one second.