Novel mechanism for creating long-lived metastable atomic negative ions

A novel mechanism is proposed for creating long-lived metastable atomic negative ions in complex atoms. It exploits the orbital collapse of the 5d orbital in Gd (Z=64) into the 4f orbital of Tb (Z=65). In the region of collapse the properties of the 5d and 4f orbitals are quite sensitive to the changes in the effective potential. Consequently the collapse phenomenon impacts significantly the core-polarization interaction in the relevant atoms. The mechanism is demonstrated in Tb and Dy through the appearance of long-lived Tb⁻ and Dy⁻ anions in the Regge-pole calculated electron elastic cross sections. (paper)