Abstract
Nuclear-spin-symmetry conservation makes the observation of transitions between quantum states of ortho- and para- extremely challenging. Consequently, the energy-level structure of derived from experiment consists of two disjoint sets of level energies, one for para- and the other for ortho-. We use a new measurement of the ionization energy of para- [] to determine the energy separation [] between the ground states of para- and ortho- and thus link the energy-level structure of the two nuclear-spin isomers of this fundamental molecule. Comparison with recent theoretical results [M. Puchalski et al., Phys. Rev. Lett. 122, 103003 (2019)] enables the derivation of an upper bound of 1.5 MHz for a hypothetical global shift of the energy-level structure of ortho- with respect to that of para-.
- Received 18 July 2019
DOI:https://doi.org/10.1103/PhysRevLett.123.163002
© 2019 American Physical Society