Quenching of auroral hydrogen line emission by collisional ionization

With the aid of the classical impulse approximation a simple formula is derived for the cross section for electron loss from fast excited hydrogen atoms passing through a neutral gas. Detailed computations relevant to the quenching of hydrogen line emission in auroras are performed. It is found, incidentally, that the population distribution amongst the states of a level is unlikely to be brought into statistical equilibrium by the collisions suffered by the hydrogen atoms.