J. Phys. B: At. Mol. Opt. Phys. 30 (1997) 1179–1189. Printed in the UK PII: S0953-4075(97)77232-8 Three-step laser excitation of the 6p 3/2 ns, nd J = 1, 2, 3 autoionizing Rydberg levels of lead S A Bhatti†, M Nawaz†, S M Farooqi†, A Ahad†, Saira Butt†, N Ahmad† and M A Baig‡ † Applied Physics Division, PINSTECH, PO Nilore, Islamabad, Pakistan ‡ Atomic and Molecular Physics Laboratory, Department of Physics, Quaid-i-Azam University, 45320 Islamabad, Pakistan Received 15 August 1996, in final form 5 November 1996 Abstract. We report here first measurements of the odd-parity 6p 3/2 ns J = 1, 2 and 6p 3/2 nd J = 0, 1, 2, 3 autoionizing Rydberg levels of lead using a three-step laser excitation scheme in conjunction with an atomic beam apparatus. Four initial levels 6p 3/2 7p 1/2,3/2 J = 1, 2 were chosen for the excitation of the final levels. The assignments have been made using the j 1 K-coupling scheme for the observed levels. The Rydberg series 6pnd3/2[1/2] 0,1 (13  n  38),3/2[3/2] 2 (16  n  73),3/2[5/2] 2,3 (13  n  37) and 3/2[7/2] 3 (16  n  39) as well as 6p 3/2 ns3/2[3/2] 1,2 (14  n  40) are reported. All the observed series exhibit constant quantum defects with respect to the ionization potential value 73 900.65 ± 0.05 cm −1 . The full widths at half the maximum Ŵ of the observed levels are also reported. 1. Introduction The atoms in the fourth group of the Periodic Table have two valence electrons with p 21 S 0 ground-state configuration and zero angular momentum cores. However, unlike the second- group elements which also possess two electrons in the valence shell with s 21 S 0 ground- state configuration and zero angular momentum cores, the fourth-group elements have not attracted much attention from the spectroscopists, especially from those who use the laser spectroscopic techniques. In particular, very little spectroscopic data exist above the first ionization limit. We have chosen lead, the heaviest in the fourth group, but relatively more friendly than the others in the group from an experimentalists’s point of view. The optical spectra of lead have been extensively studied using the conventional spectroscopy (Garton and Wilson 1966, Wood and Andrew 1968, Moore 1971, Brown et al 1977, Griesmann et al 1991) and using the laser spectroscopic techniques (Bolshov et al 1977, Young et al 1980, Buch et al 1988, Ding et al 1989, Dembcyznski et al 1994, Farooqi et al 1995, Hasegawa and Suzuki 1995). However, it is the work of Brown et al (1977) which has produced the most comprehensive data between the first and the second ionization limits of lead. Since the data were obtained by conventional absorption spectroscopy, the total angular momentum quantum number, J , of the observed levels is equal to 1. Using the laser spectroscopy techniques Bolshov et al (1977) observed the odd parity levels of the 6p 1/2 nℓ series (16  n  67,ℓ = 0, 2, 4). Young et al (1980) and Ding et al (1989) reported the even parity 6p 1/2 np and 6p 1/2 nf J = 0–2 levels using a single dye laser. Recently, Farooqi et al (1995) and Hasegawa and Suzuki (1995) reported the even parity 6p 1/2 np and 6pnf J = 0–2 levels using the multistep-laser excitation technique. So far, to our 0953-4075/97/051179+11$19.50 c  1997 IOP Publishing Ltd 1179