Eur. Phys. J. D 46, 437–442 (2008) DOI: 10.1140/epjd/e2008-00010-x T HE EUROPEAN P HYSICAL JOURNAL D High resolution measurement and MQDT analysis of the 5d 9 6s 2 np, nf (J = 1) autoionizing resonances of mercury M.A. Baig 1, 2, a 1 Atomic and Molecular Physics Laboratory, Quaid-i-Azam University, 45320 Islamabad, Pakistan 2 Physikalisches Institut, Universit¨at Bonn, Nussallee 12, 53115 Bonn, Germany Received 2 October 2007 / Received in final form 13 November 2007 Published online 23 January 2008 – c  EDP Sciences, Societ`a Italiana di Fisica, Springer-Verlag 2008 Abstract. We report new high resolution photoabsorption measurements of the 5d-subshell excitation spec- tra of mercury using a 3-meter normal incidence spectrograph equipped with a 6000 line/mm holographic grating and synchrotron radiation emitted by the Bonn 2.5 GeV electron accelerator as the background source of continuum. The observed spectra reveal autoionizing resonances attached to the 5d 9 ( 2 D 5/2 )6s 2 and 5d 9 ( 2 D 3/2 )6s 2 parent ion levels of mercury. We have analysed the line shapes of the lower members of the 5d 9 6s 2 np and nf J = 1 autoionizing resonances using the phase shifted formulation of the MQDT and extracted the interaction parameters. PACS. 32.70.Jz Line shapes, widths, and shifts – 32.80.-t Photon interactions with atoms – 32.80.Dz Autoionization – 32.80.Fb Photoionization of atoms and ions 1 Introduction The absorption spectrum of mercury above the first ion- ization threshold is dominated by the autoionizing res- onances due to 5d-subshell excitation. Adjacent to the ionization limit, there exist the leading members of the series attached to the 5d 3/2 ionic level designated as 5d6p 3 P 1 and 3 D 1 respectively whereas the leading member of the 5d 5/2 6p 1 P 1 series lies below the first ionization limit and perturbs the principal and inter-combination 6snp 1 P 1 and 3 P 1 series. The spectrum of mercury in the autoionization region has been extensively studied using the photoabsorption technique (Beuttler [1], Marr and Auston [2], Garton and Connerade [3], and Cairns et al. [4], Mansfield [5], Baig [6]). The relative and total photoionization cross sections in the autoionization region was obtained by Brehm [7], Brehm and Hofler [8] and Berkowitz and Lifshitz [9,10]. Dehmer and Berkowitz [11] obtained the partial cross sections for the 6s 2 S 1/2 , 5d 2 D 5/2 and 2 D 3/2 ionic states using the branching ratios together with the normalized total photoionization cross section of Cairns et al. [4], while the partial relative cross section for the individual 6s 2 S 1/2 ,5d 2 D 5/2 and 2 D 3/2 states have been measured by M¨ uller et al. [12]. Martin et al. [13] applied the Slater-Condon theory with configuration interaction to calculate the positions of the energy levels in mercury. Forrest et al. [14] studied the autoionizing states of mercury by electron impact ex- citation and proposed numerous new assignments to the a e-mail: baig@qau.edu.pk levels of 5d 9 6s 2 ns,5d 9 6s 2 6d,5d 10 6p 2 and 5d 9 6s 2 7s config- urations, based on both theoretical calculations and quan- tum defect series analysis. The measurement of the spin polarization of photoelectrons in the autoionization region using circularly polarized synchrotron radiation and us- ing un-polarized light from rare gas discharge lamps were reported by Sch¨ afers et al. [15]. The experimental data on the photoabsorption cross section and angle resolved photo-electron spin polarization for mercury have been presented by Sch¨ onhense et al. [16]. M¨ uller et al. [12] con- ducted the spin-polarization measurement in the autoion- ization region and investigated the angle-resolved photo- electrons between the 5d 9 6s 22 D 5/2 and 2 D 3/2 thresholds. Bartschat and Scott [17] theoretically calculated the to- tal cross section of mercury in the energy range 10.43 eV to 14.0 eV and also reported the asymmetry parame- ter (β) for the angular distribution of photoelectrons. Ding et al. [18] employed the two-colour laser spectro- scopic technique to excite the inner valence shell spec- trum of mercury and observed the multiplet splitting for the 5d 9 nf states. Sch¨ afers et al. [19] reported a multichan- nel quantum-defect analysis of the experimental data on the spin-polarization for 6s dipole transition amplitudes and phase shift differences for photoionization of 5d and 6s shells. Recently, Toffoli et al. [20] applied the relativis- tic time dependent density-functional theory to the pho- toionization of mercury and calculated the partial cross sections and asymmetry parameter profiles for the 6s,5d, 5p and 4f sub-shells and compared with the earlier rela- tivistic random phase approximation (RPA) calculations.