Two-step laser optogalvanic spectroscopy of the odd-parity Rydberg states of atomic mercury M. A. Zia and M. A. Baig Eur. Phys. J. D, 28 3 (2004) 323-330 Published online: 20 January 2004 DOI: 10.1140/epjd/e2003-00325-0