Hyperfine Suppression of $2^3{\rm S}_1 - 3^3{\rm P}_J$ Transitions in $^3$He

TL;DR

This paper investigates the hyperfine suppression of specific atomic transitions in helium-3, revealing that hyperfine interactions drastically weaken certain transitions and proposing an alternative coupling model to explain this phenomenon.

Contribution

The study identifies and measures extremely weak transitions in helium-3 and introduces an extit{IS}-coupling model to explain hyperfine suppression effects.

Findings

Transition strengths are 1,000 times weaker than the strongest transition.

Hyperfine interaction dominates over fine structure in suppressing transitions.

The extit{IS}-coupling model explains the observed transition strengths.

Abstract

Two anomalously weak transitions within the $2 ^3{\rm S}_1~-~3 ^3{\rm P}_J$ manifolds in $^3$He have been identified. Their transition strengths are measured to be 1,000 times weaker than that of the strongest transition in the same group. This dramatic suppression of transition strengths is due to the dominance of the hyperfine interaction over the fine structure interaction. An alternative selection rule based on \textit{IS}-coupling (where the nuclear spin is first coupled to the total electron spin) is proposed. This provides qualitative understanding of the transition strengths. It is shown that the small deviations from the \textit{IS}-coupling model are fully accounted for by an exact diagonalization of the strongly interacting states.