Rotational Splittings in Diatomic Molecules of Interest to Searches for New Physics

2025/11/07 by Sunaga, Ayaki, Fleig, Timo
#Atomic Physics (physics.atom-ph) #FOS: Physical sciences

paper · doi:10.48550/arxiv.2511.05189

Abstract

Diatomic molecules with an energetically low-lying ³ Δ₁ 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 Δ₁ state is its tiny Λ-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 Λ-splitting is helpful for planning new experiments. In this study, we present a theoretical model to calculate the Λ-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 Λ-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.

Citations

• Nuclear Electric Quadrupole Moment-Induced Parity Doubling in Molecules for Symmetry-Violation Searches
• Quantum logic control and precision measurements of molecular ions in a ring trap -- a new approach for testing fundamental symmetries

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