Rotational Splittings in Diatomic Molecules of Interest to Searches for New Physics
Abstract
Diatomic molecules with an energetically low-lying 3 1 state are attractive platforms to detect new physics beyond the Standard Model, such as parity- and time-reversal violating phenomena. One of the advantages of using a 3 1 state is its tiny -splitting due to the coupling between the electronic and rotational angular momenta, which facilitates polarizing the molecules in small external electric fields. Theoretical estimation of the magnitude of the -splitting is helpful for planning new experiments. In this study, we present a theoretical model to calculate the -splitting. Our model integrates the relativistic four-component wavefunction and the traditional rotational Hamiltonian based on Hund's case (a). The multireference character of the wavefunction is taken into account. Our calculations for PtH and ThF+ molecules qualitatively agree with experiment. The -splitting of TaO+ for the rotational ground state is predicted to be around 9 kHz. This tiny splitting can reduce the systematic uncertainty, but in a practical experiment, it may cause depolarization during rotation ramp-up.
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