A Fortran program (tlchng.f) to calculate Maxwellian rate coefficients for
l-changing atomic collisions, i.e. those where the transition energy delta-e is
approx zero. e.g. n l1->n l2, where l2=l1+/-ld and ld=1 for dipole transitions.

It gives results for the quantum mechanical (QM) approximation detailed by
Vrinceanu et al (2012) and (for dipole only) compares them with the results 
given by the modified Pengelly & Seaton approximation (PSM20) of
Badnell et al (2021) which, in extreme cases, improves-upon the original modified
Pengelly & Seaton approximation (PSM17) introduced by Guzman et al (2017).

The program tlchng.f is self-contained, just compile and execute.
The interactive driver should be self-explanatory.

The driver wrapper can be discarded and the SUBROUTINE LCHNG (plus its dependencies)
can be incorporated into users' own codes.
The driver illustrates the data that needs to be provided to SR.LCHNG and its output.

In addition, the stripped-down Fortran program (tpsmx.f) evaluates just the analytic
expressions for the various (Modified) Pengelly & Seaton approximations. Similarly,
SUBROUTINE PSMX (plus its dependencies) can be incorporated into users' own codes.


REFERENCES:
Badnell N. R., Guzman F., Brodie S., Williams R. J. R., van Hoof P. A. M., Chatzikos M., 
               Ferland G. J., 2021 MNRAS, 507, 2922
Guzman F., Badnell N. R., Williams R. J. R., van Hoof P. A. M., Chatzikos M., 
               Ferland G. J., 2017 MNRAS, 464, 312
Pengelly R. M., Seaton M. J., 1964, MNRAS, 127, 165
Vrinceanu D, Onofrio R., Sadeghpour H. R., 2012 ApJ, 747, 56