Very highly excited bound states of atomic negative ions having all their electrons with unpaired spins

Abstract

By identifying a special class of atomic negative ion states where all electron spins are unpaired and where the nuclear charge is partially unscreened, we predict, via large-scale state-specific calculations, that B − , C − , N − and O − have states which belong to the discrete spectrum even though they are very highly excited and embedded in a multitude of ionization thresholds. For example, the O − 1s2s2p 3 3s3p 3 10 S state lies 600.6 eV above the O 1s 2 2s 2 2p 4 3 P ground state and yet it is bound. For N − , the two maximum spin states, 1s2s2p 3 3s3p 2 9 P o and 1s2s2p 3 3p 3 9 S, are connected by an electric dipole transition with λ = 4615.5 Å and with transition rate ∼ 2.7 × 10 8 s −1 . For these unique states, the reliable prediction of the relevant energy differences demanded the execution of systematic all-electron calculations, with interand intra-shell correlations included.

Reexamining if long-livedN−anions are produced in fast dissociative electron-capture collisions

“…The lifetime Cowan et al [11] calculated for the unstable 3 P ground state of N − , 38 fs, is in excellent agreement with the measurements of Mazeau et al [13,14]. In contrast to the short lifetimes of the low-lying excited states, low-lying maximum spin states, namely, the highly excited ͑1s 2s 2p 3 3s 3p 2 ͒ 9 P o and ͑1s 2s 2p 3 3p 3 ͒ 9 S states of N − embedded in the continuum, were predicted to be stable against autodetachment by Piangos and Nicolaides [15]. Their findings also suggests that highly excited states with high spin, though below the maximum value, might be long lived.…”

“…We revisited our earlier work motivated by the recent publications [11,[16][17][18], and the renewed interest in long lived N − , mainly driven by the impact of long lived N − on carbon dating. Repeating our measurements was further motivated by the new theoretical prediction of stable maximum-spin states of N − , thus suggesting that there are long lived highspin states [15]. Therefore, high-spin states of N − provide a new interpretation of our "old" measurements of long lived N − .…”

“…This, together with the studies of Muller et al [16,17], which set an upper limit of 200 ns on the mean lifetime, and the calculated short lifetimes of the 2p 4 1 D and 1 S states (130 and 70 ps, respectively) of Cowan et al [11], suggest that these metastable states of N − would not interfere with AMS carbon dating measurements. The production of the predicted [15] stable maximum spin states or long-lived high-spin states of N − most likely requires a different mechanism than dissociative electron capture studied in this work. One such mechanism is multielectron capture from a spinaligned surface by bare nitrogen.…”

Low-level 14C measurements and Accelerator Mass Spectrometry

“…At a level of 14 C/C lower than about 10 −18 the negative ion of nitrogen may appear as the predicted metastable 9 S state of N − [23]. This is analogous to the He − ion in that all the electrons have their spins parallel.…”

Ab Initio Many-Electron Calculation of Hyperfast Time-Resolved Coherent Excitation and Decay Of Polyelectronic Atoms

“…The second category of ANI excited states are the bound excited states, whose energy is sharp, e.g., [26,28,29] and refs therein. By bound we mean that the state belongs to the nonrelativistic discrete spectrum and not that it is completely stable against radiative or relativistic nonradiative decay, unless of course its energy is below that of the ground state of the neutral atom.…”