Hyperfine and<b><i>PT</i></b>-odd effects in YbF

Abstract

Molecular spectroscopy is a sensitive probe of fundamental interactions because of the close energy spacing of hyperfine spin-rotational levels. The paramagnetic radical YbF is the subject of current experimental activity in the search for a permanent electric dipole moment of the electron, the existence of which is suggested by particle physics models beyond those described by electroweak theory. We calculate electronic matrix elements of interactions which violate both parity- and time-reversal symmetry using ab initio relativistic molecular quantum mechanics. The accuracy of our approach is assessed by performing calculations of the hyperfine structure of YbF, and comparing our results with experiment.