Pump-probe photoelectron velocity-map imaging of autoionizing singly excited 4s~14p~6 np~1(n ~= 7,8)and doubly excited 4s~24p~45s~1 6p~1 resonances in atomic krypton

摘要

Pump-probe photoelectron velocity-map imaging, using 27-eV high-harmonic excitation and 786-nmionization, is used to resolve overlapping autoionizing resonances in atomic krypton, obtaining two-photonphotoelectron angular distributions (PADs) for singly and doubly excited states. Two features in the photoelectronspectrum are assigned to singly excited 4s~1 4p~6 np~1 (n =7,8) configurations and four features provide informationabout double excitation configurations. The anisotropy parameters for the singly excited 7p configuration aremeasured to be β_2 = 1.61 ± 0.06 and β_4 = 1.54 ± 0.16 while the 8p configuration gives β_2 = 1.23 ± 0.19and β_4 =0.60 ± 0.15. These anisotropies most likely represent the sum of overlapping PADs from states ofsinglet and triplet spin multiplicities. Of the four bands corresponding to ionization of doubly excited states, twoare assigned to 4s~24p~45s~16p~1 configurations that are probed to different J-split ion states. The two remainingdoubly excited states are attributed to a previously observed, but unassigned, resonance in the vacuum-ultravioletphotoabsorption spectrum. The PADs from each of the double excitation states are also influenced by overlapfrom neighboring states that are not completely spectrally resolved. The anisotropies of the observed doubleexcitation states are reported, anticipating future theoretical and experimental work to separate the overlappingPADs into the state resolved PADs. The results can be used to test theories of excited state ionization.