Laboratory of Physical Chemistry, ETH Zurich, CH-8093 Zurich, Switzerland.
Phys Rev Lett. 2018 Jan 26;120(4):043001. doi: 10.1103/PhysRevLett.120.043001.
Measuring spin-rotation intervals in molecular cations is challenging, particularly so when the ions do not have electric-dipole-allowed rovibrational transitions. We present a method, based on an angular-momentum basis transformation, to determine the spin-rotational fine structure of molecular ions from the fine structure of high Rydberg states. The method is illustrated by the determination of the so far unknown spin-rotation fine structure of the fundamentally important He_{2}^{+} ion in the X ^{2}Σ_{u}^{+} state. The fine-structure splittings of the v^{+}=0, N^{+}=1, 3, and 5 levels of He_{2}^{+} are 7.96(14), 17.91(32), and 28.0(6) MHz, respectively. The experiment relies on the use of single-mode cw radiation to record spectra of high Rydberg states of He_{2} from the a ^{3}Σ_{u}^{+} metastable state.
测量分子离子的自旋-转动间隔具有挑战性，特别是当离子没有允许的电偶极子转动跃迁时更是如此。我们提出了一种基于角动量基变换的方法，从高里德堡态的精细结构中确定分子离子的自旋-转动精细结构。该方法通过确定迄今为止未知的 X ^{2}Σ_{u}^{+}态下基本重要的 He_{2}^{+}离子的自旋-转动精细结构来加以说明。He_{2}^{+}离子 v^{+}=0，N^{+}=1，3 和 5 能级的精细结构分裂分别为 7.96(14)，17.91(32)和 28.0(6)MHz。该实验依赖于使用单模连续波辐射从 a ^{3}Σ_{u}^{+}亚稳态记录 He_{2}的高里德堡态的光谱。
