Jhd. Eland et al., DOUBLE PHOTOIONIZATION OF H2S BELOW THE DOUBLE-IONIZATION POTENTIAL, Journal of physics. B, Atomic molecular and optical physics, 30(9), 1997, pp. 2177-2186
Three separate experiments demonstrate that an indirect process of dou
ble ionization can populate part of the potential energy surface of th
e H2S2+ ion at energies below the lowest bound vibrational level. The
process seems to involve autoionization at a curve crossing of a singl
y ionized (or possibly neutral) state with a repulsive part of the adi
abatic ground state doubly charged ion surface.