Autoionizing States in Highly Ionized Oxygen, Fluorine, and Silicon
Excitation processes in atoms or ions usually involve the promotion of one of the least tightly bound outer shell electrons to a higher orbital leading to a state lying below the ionization threshold. It is possible however to form highly excited discrete states that are embedded in the continuum if one or more inner core electrons are raised to outer shells. In the present paper we report on such states in high Z 3-electron ions associated with core excited configurations of the type 1s2snl and 1s2pnl. Such states may autoionize rapidly via the Coulomb interaction unless forbidden to do so by selection rules on this process. These metastable autoionizing states either decay by radiation or autoionize at a slower rate via the weaker magnetic interactions. The lowest lying quartet state in 3-electron ions (1s2s2p)4P 5/2 o is metastable against both autoionization and radiation. Our previously measured lifetimes  for this state (in nanoseconds) are: S (1.1), Si (2.1), Ar (0.66), Cl (0.91), F (15), and 0 (25). Radiative decay processes involving core-excited states have also been previously observed. For example, one type of decay is an El transition between two metastable quartet states and another is a similar transition from a core excited state to a singly excited state.
KeywordsQuartet State AUTOIONIZING State Foil Target Outer Shell Electron Cylindrical Mirror Analyzer
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