Photoionization time delay of Hg 6s subshell at higher energies: RMCTD calculations

The study of photoionization of atomic mercury highlights the importance of electron correlation in high-Z atoms [1-3]. Attosecond time delay [4-5] in photoionization processes [4] is an excellent probe to understand the dynamics of the highly correlated atomic systems. Earlier studies have shown that dipole and quadrupole photoelectron angular distributions are dramatically affected near the 6s dipole Cooper minimum in atomic mercury [2]. Photoionization time delay has been reported [6] in the near threshold region of 6s using the relativistic-random-phase approximation (RRPA) [7], RRPA with relaxation (RRPA-R) [8] and the relativistic multiconfiguration Tamm Dancoff approximation (RMCTD) [9, 10] techniques and the time delay was found to be very sensitive to how correlations are treated. The present work reports the 6s photoionization cross section, photoelectron angular distribution and Wigner time delay using RMCTD [11] in the energy region well above the 6s threshold near the second Cooper minimum (~130 eV) and non-RPA correlations [10] that are included in RMCTD are found to be important. Significant time delay is predicted in Hg 6s in the region of second Cooper minimum. [1] D. Toffoli, et al., Phys. Rev. A 66, 012501 (2002); [2] T. Banerjee, P.C. Deshmukh and S.T. Manson, Phys. Rev. A 75, 042701 (2007); [3] B. H. McQuaide, et al., Phys. Rev. A 35, 1603 (1987) [4] A. S. Kheifets and I. A. Ivanov, Phys. Rev. Letts. 105, 233002 (2010); [5] P.C. Deshmukh et al., Phys. Rev. A 89, 053424 (2014); [6] A. Ganesan et al., BAPS 60(7), 128 (2015); [7] W. R. Johnson and C. D. Lin. Phys. Rev. A 20, 964 (1979); [8] V. Radojevic, et al., Phys. Rev. A 40, 727 (1989); [9] V Radojevic and W. R. Johnson, Phys. Rev. A 31, 2991 (1985); [10] J. Jose, et al., Phys. Rev. A 83, 053419 (2011).