Tunneling ionization of Rydberg molecules

The theory of tunneling ionization of atoms is generalized to ionization of symmetric top molecules, either polar or nonpolar. Low-lying excited states of molecules, for which the ordinary Born-Oppenheimer approximation holds, and high-lying excited states, for which the inverse Born-Oppenheimer approximation holds, are discussed. Ionization in a constant external field is analyzed, as is ionization in an alternating field. It is shown that the orientation of the molecule's axis along the held does not lead to any appreciable increase in the ionization probability as compared to other orientations. (C) 1997 American Institute of Physics.