Atomic structure

The analysis of atomic spectra, term analysis, has a long history at Lund University and a worldwide reputation. The goal of a term analysis is to determine the atomic structure of a species, i.e. to find the excitation energies of the various energy levels in an atom or atomic ion relative to the most bound state, the ground state. The energy difference between two levels can be measured as the frequency (or wavelength) of the corresponding transition (spectral line) either in absorption or emission. The final result is a set of energy levels, with measured energies and the labels given with a proper spectroscopic notation.

Fig 1. Part of the Mo II term system, split up in subconfigurations, 4d⁴(^ML)nl, where ^ML is the parent term.

An observed spectral feature may show a small-scale pattern due to hyperfine structure (hfs) or isotope shift (IS). Both are effects of the atomic nucleus. Hfs is an internal atomic interaction between the electrons and the nuclear spin, and IS is a result of a small difference in the transition wavelength for different isotopes of an ensemble of atoms.

Fig 2. Hyperfine structure in Pr II.

Our term analyses have during the last decades been focused on neutral, singly and doubly ionized atoms of the transition elements and rare earth elements.