Search for long-lived states of the heavier rare gas negative ions

A pure quartet state is expected in the energy spectrum of all the heavier rare gas negative ions which is metastable for autoionization to the ground state of the neutral atom. If this state occurs below the energy of the parent np5(2P3/2)(n + 1)s[3/2] state then it may be possible to produce accelerated beams of the heavier rare gas negative ions as is now done using the (1s2s2p)4P state of He−. A search was made for the negative ions Ne−, Ar−, Kr−, and Xe− following double electron capture in a krypton target at energies near 50 and 100 keV in the energy range where the He+ double charge exchange cross section is at its maximum. No definite evidence was found for any of these heavier rare gas negative ions, and they must all therefore have lifetimes less than 10−6 s.