Laboratorium für Physikalische Chemie, ETH Zürich, 8093 Zürich, Switzerland.
Department of Physics and Astronomy, LaserLaB, Vrije Universiteit Amsterdam, de Boelelaan 1081, 1081 HV Amsterdam, Netherlands.
Phys Rev Lett. 2019 Oct 18;123(16):163002. doi: 10.1103/PhysRevLett.123.163002.
Nuclear-spin-symmetry conservation makes the observation of transitions between quantum states of ortho- and para-H_{2} extremely challenging. Consequently, the energy-level structure of H_{2} derived from experiment consists of two disjoint sets of level energies, one for para-H_{2} and the other for ortho-H_{2}. We use a new measurement of the ionization energy of para-H_{2} [E_{I}(H_{2})/(hc)=124 417.491 098(31) cm^{-1}] to determine the energy separation [118.486 770(50) cm^{-1}] between the ground states of para- and ortho-H_{2} 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)PRLTAO0031-900710.1103/PhysRevLett.122.103003] enables the derivation of an upper bound of 1.5 MHz for a hypothetical global shift of the energy-level structure of ortho-H_{2} with respect to that of para-H_{2}.
核自旋对称守恒使得观察正氢和仲氢的量子态之间的跃迁变得极具挑战性。因此，实验得出的 H_{2} 的能级结构由两组不相交的能级组成，一组用于仲氢，另一组用于正氢。我们利用对仲氢的电离能的新测量值[E_{I}(H_{2})/(hc)=124 417.491 098(31) cm^{-1}]来确定正、仲 H_{2} 的基态之间的能量间隔[118.486 770(50) cm^{-1}]，从而将这个基本分子的两种核自旋异构体的能级结构联系起来。与最近的理论结果的比较[M. Puchalski 等人，Phys. Rev. Lett. 122, 103003 (2019)PRLTAO0031-900710.1103/PhysRevLett.122.103003]使我们能够得出一个上限，即假设正 H_{2} 的能级结构相对于仲 H_{2} 发生整体移动，其移动幅度的上限为 1.5 MHz。
