Accurate Gaunt factors for non-relativistic quadrupole bremsstrahlung
  The exact result for non-relativistic quadrupole bremsstrahlung in a Coulomb
field was established only recently in Pradler & Semmelrock (2020). It requires
the evaluation and integration of hypergeometric functions across a wide range
of parameters and arguments, which, in practice, is unfeasible. Here we provide
a highly accurate tabulation of the Gaunt factor for quadrupole radiation, its
thermal average in a Maxwellian plasma, and the associated cooling function
over the entire kinematically relevant range. In addition, we provide a simple
approximate formula for the emission cross section which works to within a few
percent accuracy for all practical purposes. The results can be applied to the
scattering of electrons with themselves, for which quadrupole radiation is the
dominant process.
