Unexpected transitions induced by spin-dependent, hyperfine and external magnetic-field interactions

Abstract

Unexpected transitions are induced by weaker interactions not included in the gross structure model of the ion under investigation. We discuss different examples of such decay channels, starting with relativistic spin-induced transitions. These represented an important field of study a few decades ago, and we illustrate how some challenging cases can be treated very accurately with todayʼs computational techniques, while close degeneracy sometimes still prevents ab initio methods from obtaining accurate results. For hyperfine induced transitions we review some recent results and discuss remaining challenges for experiment and theory. Finally, we discuss the newly opened field of accurate calculations for transitions induced by an external magnetic field and point to some examples of where these are accessible for experimental tests.

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

“…The M1 is a forbidden transition, but expected [15,16], since it is not induced by small corrections to the wavefunction. More importantly, the rate of the M1 transition in this model, does not depend on the radial part of the wavefunctions, but is rather given by [17] …”

Magnetic-field- and hyperfine-induced P03−S01 transitions in Be- and Ne-like ions

“…To derive induced transition rates, we need to calculate the transition probabilities in Eq. (20) as well as the hyperfine and magnetic interaction matrix elements [2]. The transition rates can be expressed in both the Babushkin and Coulomb gauges [47].…”

“…There are a wide range of calculations for hyperfineinduced transitions (HIT) [3,12,[14][15][16]19,20,39,42] and magnetic-field-induced transitions for isotopes without nuclear spin (MIT-fs) [2,6,8]. Here, we focus on discussing the magnetic-field-and hyperfine-induced (MIT-hfs) transitions for isotopes with nuclear spin.…”

“…Unexpected transitions [1,2], e.g., spin-, hyperfine-(HIT), and magnetic-field-induced (MIT) transitions, are important in the diagnostics of different plasmas since they are sensitive and unique tools for the determination of, e.g., electron densities, isotope compositions, and magnetic fields [3][4][5]. These transitions pose a challenge to computations since their predictions often require a careful and thorough treatment of the atomic structure.…”

Advanced multiconfiguration methods for complex atoms: I. Energies and wave functions

“…If data for atomic transitions are known, the spectra from the plasma can give information about its fundamental properties, e.g., temperature and density (if they are well-defined), as well as the abundance of different elements and the balance between different ionization stages [18]. In some cases we are also able to determine magnetic fields -their strengths and polarization [19,20]. In cases where the plasma is not in what is referred to as Local Thermal Equilibrium (LTE), even stronger demands are put on the atomic data, to be used in modeling [21,22].…”