Microwave ionization of Rydberg states of the barium ion M. Seng, U. Eichmann, V. Lange, T. F. Gallagher and W. Sandner Eur. Phys. J. D, 3 1 (1998) 21-27 Published online: 15 July 1998 DOI: 10.1007/s100530050145