Classical calculation of radiative decay rates of hydrogenic Stark states

The Kepler-Coulomb problem is solved in parabolic coordinates and the Larmor radiation problem is analyzed to complement a previous study performed for the usual representation in spherical polar coordinates. A comparison with quantum spontaneous decay rates shows that for azimuthal quantum number $m = 0$ states only transitions to nearby $n-\Delta n$ principal quantum number states are described properly by the Wentzel-Kramers-Brillouin quantized classical motions, but that for $m > 0$ reasonable results emerge for many values of $\Delta n$. A simple approximate expression for the lifetime of $m \ne 0$ states emerges from the semi-classical analysis.