Resolving a discrepancy between experimental and theoretical lifetimes in atomic negative ions

Abstract

Recently the lifetime of the excited 2 P 1/2 -state of S − was measured to be 503 ± 54 s (Bäckström et al. Phys. Rev. Lett. 114, 143003 (2015)). The earlier theoretical lifetime of 436 s was clearly outside the experimental error bars. To investigate this discrepancy we have performed systematic and large-scale multiconfiguration Dirac-Hartree-Fock calculations for this system. After including a careful treatment of correlation and relativistic effects, we predict a well-converged value of 492 s for this lifetime, with an uncertainty considerably less than 1%, thereby removing the apparent conflict between theory and experiment. We also show that this result corresponds to the nonrelativistic limit in the LS-approximation for the M1 transition within this 2 P term. We also demonstrate the usefulness of the latter approach for 2 P transitions in O − , Se − and Te − , as well as for analogous M1 transitions within 2 D terms in Ni − and Pt − ions.

High-precision electron affinity of oxygen

“…( 1 ) for the s -wave) that can be determined with high precision 31 , 32 . However, the upper fine-structure level of O − has a lifetime of several hours 33 ; any population in this level will thus normally cause a photodetachment signal below the electron affinity threshold, giving rise to a large background.…”

Ab initio MCDHF calculations of the In and Tl electron affinities and their isotope shifts

“…The quality of the transition energies is however an important ingredient due to the λ 3 scaling factor appearing in the M1 spontaneous emission A rate. For this reason, we also report the adjusted lifetimes to the experimental excitation energies [44], measured in the LPTS [17] experiment. The resulting lifetimes of a few hundreds of seconds, could be measured in a cryogenic ion storage ring that was demonstrated to be efficient to store negative ion beams in the hour time domain [41,42].…”

A summary of results obtained with the cryogenic electrostatic storage ring DESIREE

“…In contrast to fine structure M1 transitions in e.g. S -, Se -, and Te -, such lifetimes may not be easily predicted from experimentally determined or precisely calculated transition energies [22]. Laser probing techniques may also be used to determine the rotational temperature of molecular ions that have been stored for long enough time to relax to their vibrational ground states.…”

“…These are important benchmarkers for theoretical methods treating electron correlation effects (for more details and recent theoretical results see e.g. Ref[22] and references therein).…”