Long-wave instability of an ionization front

We consider the corrugation instability of a plane, subsonic, stationary ionization front, whose motion is maintained by the flux of ionizing radiation incident normally to its surface. The behavior of the gas on either side of the front is assumed to be isothermal. Unstable modes of the front corrugation with wavelengths that exceed the recombination length in the ionized region were detected. The agreement between our results and the previous studies and observations is discussed.