High-resolution spectroscopy of barium monofluoride: Odd isotopologues, hyperfine structure and isotope shifts

TL;DR

This study combines theoretical calculations and high-resolution spectroscopy to analyze BaF isotopologues, revealing hyperfine structures, isotope shifts, and nuclear charge radii differences, aiding precision measurements and laser cooling techniques.

Contribution

It provides the first detailed comparison of ab initio calculations with experimental spectra for BaF isotopologues, especially the odd ones, and offers insights into nuclear structure and laser cooling.

Findings

Hyperfine and rovibrational spectra of BaF isotopologues characterized.

Isotope shifts analyzed, revealing odd-even nuclear charge radii staggering.

Benchmark data supports future precision measurements and laser cooling applications.

Abstract

Barium monofluoride (BaF) is a promising molecular species for precision tests of fundamental symmetries and interactions. We present a combined theoretical and experimental study of BaF spectra and isotope shifts, focusing in particular on the poorly understood odd isotopologues 137BaF and 135BaF. By comparing state-of-the-art ab initio calculations with high-resolution fluorescence and absorption spectroscopy data, we provide a benchmark for electronic structure theory and disentangle the hyperfine and rovibrational spectra of the five most abundant isotopologues, from 138BaF to 134BaF. The comprehensive knowledge gained enables a King plot analysis of the isotope shifts that reveals the odd-even staggering of the barium nuclear charge radii. It also paths the way for improved laser cooling of rare BaF isotopologues and crucially supports future measurements of nuclear anapole and Schiff moments.