Theoretical evaluation of the^7,9Be 2s2p²⁴P_1/2,3/2,5/2hyperfine structure parameters and Be 2s2p³P^oelectron affinity

Abstract

The hyperfine structures of 7,9Be− 2s2p2 4P 1/2,3/2,5/2 are investigated theoretically using the multiconfiguration Hartree–Fock and configuration interaction methods. The effects of the hyperfine mixing between the fine-structure J-levels are discussed. The feasibility of some atomic spectroscopy experiments, allowing determination of the 7Be quadrupole moment from the observed hyperfine structure of the 7Be− negative ion and from the present electronic parameters, is investigated. The Be 2s2p 3Po electron affinity is monitored as a function of the orbital and configuration spaces to assess the reliability of the wavefunctions of the neutral atom and the negative ion. The theoretical value nicely converges towards the most recent theoretical and experimental results.

Isotope shift in the electron affinity of beryllium

“…Before revisiting theoretically the difficult case of chlorine for which the many-body calculations failed to reproduce observation, it would be interesting to investigate, both theoretically and experimentally, the isotope shift on the electron affinity of lighter systems such as lithium. We also hope that the present work, together with the theoretical work on hyperfine structures [17], will stimulate some new experiments on the negative beryllium ion for its various isotopes. Tables and table captions …”

“…The theoretical ab initio specific mass shift contribution to the electron affinity, was indeed found to be negative, and sensitively larger in absolute value than the (positive) normal mass shift contribution. This fact was confirmed through the measurements of the 17 O electron affinity by Blondel et al [15] owing to the high sensitivity of the photodetachment microscopy experiments that revealed electron images even for the rarest isotope 17 O − ion. Another interesting testcase for a comparison of theory with observation could be the isotope shift in the electron affinity of beryllium.…”

“…In the present approach we used the same largest set of one-electron orbitals optimized from the 10g-SD-MCHF expansions but extended the CI configuration space considered by Nemouchi et al [17] by including the triple and quadruple excitations up to the extra layer "8g". Table 1 shows the total energies of Be (2s2p 3 P o ) and Be − (2s2p 2 4 P ), together with the electron affinity of Be (2s2p 3 P o ) as a function of the SD-MCHF and SDTQ-CI expansions.…”

“…As it can be seen from monitoring the electron affinity value with the CI configuration spaces, the convergence has not been achieved, even with the largest CI calculations. However, it has been somewhat improved relatively to [17] and it was worthwhile to add the extra layer in the CI space. The corresponding value of 0.2876 eV (with 263 450 CSF for the negative ion) is larger than the theoretical estimation of Olsen et al [30] but the convergence trend is in line with the larger theoretical value obtained by Hsu and Chung [31] and with the most recent experimental value [32] taking into account their quoted uncertainty.…”

“…Atomic spectroscopy experiments on unstable beryllium isotopes become indeed possible owing to the ISOLDE facility at CERN [16]. Within this context, the feasibility of some experiments allowing the determination of the nuclear quadrupole moment of 7 Be from the observed hyperfine structure of the negative ion 7 Be − (2s2p 2 4 P J ) has been investigated recently [17]. In the present work we report the first ab initio calculations of the isotope shift in the electron affinity of Be (2s2p 3 P o ) for various isotopic pairs involving the 11,10,9,8,7 Be isotopes.…”