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Manuscript Title: A program to calculate radiative recombination coefficients of hydrogenic ions.
Authors: D.R. Flower, M.J. Seaton
Catalogue identifier: ACQD_v1_0
Distribution format: gz
Journal reference: Comput. Phys. Commun. 1(1969)31
Programming language: Fortran.
Computer: IBM 360/65.
Operating system: SYSTEM/360.
RAM: 2K words
Word size: 32
Keywords: Radiative recombination, Astrophysics, Hydrogenic ions, Asymptotic expansion, Kramers-gaunt factor, Radioastronomy, Plasma physics, Atomic process.
Classification: 1.4, 19.1.

Nature of problem:
Radiative recombination coefficients are required for various problems in physics and astrophysics; one such problem is the calculation of the ionization equilibria and recombination spectra of gaseous nebulae. It is desirable that the calculation of these coefficients should be completely automatic. A program has therefore been written to calculate the coefficients alphan(Z,T) for radiative recombination to energy levels of principal quantum number n of hydrogenic ions, Z being the nuclear charge and T the electron temperature. The program also calculates sums of recombination coefficients from n=n" to n=infinity. It should be noted that hydrogenic data may be used to obtain a good approximation to the recombination coefficient of non-hydrogenic ions, summed over excited states.

Solution method:
The recombination coefficients are expressed as integrals over the photo-ionization cross-sections, which are evaluated using the first three terms in the asymptotic expansion of the Kramers-Gaunt g-factor. The program is based on Seaton's paper, to which the reader is referred for a more detailed discussion of the method. The accuracy of the final results is determined by the approximation used for the g-factor and not by the numerical methods employed in the program. For (T/Z**2) <= 2 X 10**40K the maximum error in alpha1 will be 2.5% and the error aplhan for n>1 will be less than 1%. The accuracy becomes less good for higher temperatures.

It should be noted that the program does not compute coefficients, alphanl, for recombination on to individual nl states but computes only total coefficients, alphanl, for each value of n. Values of alphanl are tabulated by Burgess.

Running time:
The complete program required 12 s to compile and 1.5 s to execute the section of the test run reproduced below.