Precision Measurements Of The Electron Affinities Of Transition Metals And Lanthanides

More than 80%of the naturally occurring elements are able to form stable atomic negative ions.The excess electron in the anion is bound by the electric dipole potential induced by the polarization of the core.The short-range and shallow interaction po-tential between the electron and the atom typically supports only one bound electronic state.The polarization of the atom brings out the correlation effects between the inci-dent electron and the original ones.It can be concluded that correlation effects play a key role in determining the stability,structures and dynamics of negative ions.Correla-tion effects are usually enhanced in anions than in positive ions and atoms.Moreover,strong correlation effects do allow some atomic anions to possess bound states with opposite parities which are prerequisites to the realization of laser cooling of anions.Therefore,negative ions have rendered us better understanding of electron correlation effects in multi-electron systems.Moreover,the laser cooling of atomic anions has a potential application for sympathetically cooling antiprotons.Electron affinity(EA),reflecting the ability of an atom to accept an electron,is widely involved in plasmas physics and atmospheric chemistry.Although the exper-imental accuracies of EAs of main group elements have been gradually improved to be 0.01–0.05me V in the past several decades,few advancements in experiments about transition elements have been made.Limited by the traditional experimental methods,the uncertainties remain around 10 me V.Rare earth elements act as the least investi-gated group of elements in terms of electron affinity in the periodic table.Electronic structures of most lanthanide anions are not experimentally explored except La~-and Ce~-.Due to the fairly complicated electronic structures and weak beams of anions,the EAs of some lanthanides are still unknown.Slow electron velocity-map imaging(SEVI)method has been adopted to success-fully improve the accuracies of EAs of V and Zr by about two orders of magnitudes,and to obtain the fine structure splittings of their anions for the first time.The EAs of V and Zr were measured to be 0.52766(20)e V and 0.433284(89)e V,respectively.Moreover,a cryogenic ion trap was introduced to enhance beams of lanthanide anions and eliminate contaminations of hydrides.Photoelectron spectra of six atom-ic anions which have complicated electronic structures are well resolved by tak-ing advantage of the high resolution of SEVI method.The EAs of six elements have been measured as follows:EA(Ta)=0.328859(22)e V,EA(Ce)=0.600160(26)e V,EA(Pr)=0.10923(46)e V,EA(Nd)=0.09749(32)e V,EA(Tb)=0.13131(79)e V,EA(Lu)=0.23882(62)e V.Our work has for the first time presented the reliable exper-imental EA result for Pr and reported the first measured EA values for Nd and Tb.The accuracies of EAs of Ta and Ce have been improved by two orders of magnitudes.The binding energies of several excited bound states of anions have been measured as well.In conclusion,conducting the accurate EA measurements can not only fill the gap of Wikipedia database but also test theoretical models,thus leading better development of atomic theory.