Electron Affinity of Strontium

Abstract

We have observed a threshold in the electron photodetachment cross section of Sr ions at a photon energy hv = 1.820 eV and assign it to a p-wave transition from the 5s 5p P ground state in Sr to the Ss5p 3P state in neutral Sr. The measurement was made with a new technique combining the tunable laser photodetachment threshold method with accelerator mass spectrometry. We determine for the first time the electron affinity of Sr to be 48~6 meV, much smaller than predicted in recent calculations. The PI/2-P3/2 fine splitting of the Sr ground state is estimated to be 26~8 meV. PACS numbers: 32.10.Hq, 07.75.+h, 32.80.Fb Investigations of the stability of free negative ions provide excellent testing grounds for our understanding of the many-body problems of electrons bound to nuclei and the subtle electron correlation processes. The case of Ca, in particular, has become fascinating when, in contrast to former predictions, it was experimentally discovered to form a stable negative ion [1]. Confirmed by calculations, this state is described as a 4p electron bound to the Ca ground state to form a 4s 4p P configuration [2]. The electron affinity was then predicted to be 45 meV [2] (see also [3,4] for recent references) and measured as 43~7 meV [1]. Later experiments

State-Selective Depletion Spectroscopy of Negative Ions: First Observation of the4PState inCa−Kristensen1, Brodie2, Pedersen3 et al. 1997Phys. Rev. Lett.251120View full textAdd to dashboardCite

“…Thus it is very doubtful whether the 4 P state in Ca 2 has been observed so far [11]. The study of the Sr 2 ion has been less intensive until now, and only the existence of the ground state is established [12,13].The experiments were carried out using a collinearly overlapped negative-ion͞laser-beam setup previously described [1,11,14]. A 40 kV Ca 2 or Sr 2 beam is overlapped by three pulsed nanosecond laser beams in a 1 m long interaction region.…”

“…Thus it is very doubtful whether the 4 P state in Ca 2 has been observed so far [11]. The study of the Sr 2 ion has been less intensive until now, and only the existence of the ground state is established [12,13].…”

Self-dual supergravity from N = 2 strings

“…An alternative way to derive the low energy effective action is to compute scattering amplitudes. For N = 2 strings the most convenient way to do such calculations is to use the reformulation as N = 4 topological strings developed by Berkovits and Vafa [40] and subsequently used by Berkovits [41], Ooguri and Vafa [42]. It will be interesting to perform such a calculation not only in order to confirm the results we obtained using sigma model methods but, more importantly, to study the internal sector, which is hard to analyze using sigma model techniques.…”

Multireference many‐body perturbation theory calculations on negative ions with small electron detachment energies

“…Moreover, the corresponding neutral species cannot be considered as perfect closed‐shell systems because of strong admixture of np 2 configurations in the ground‐state wave functions. At the same time, highly accurate experimental electron affinities of alkaline–earth atoms are now available 24–26; moreover, an excellent agreement with experimental data has been achieved in ab initio relativistic many‐body perturbation calculations 6 that employed the linear cluster approximation to evaluate the correlations beyond second order.…”