Schmitz J R, Merkt F
Institute of Molecular Physical Sciences, ETH Zurich, CH-8093 Zurich, Switzerland.
Phys Chem Chem Phys. 2025 Jan 15;27(3):1310-1319. doi: 10.1039/d4cp04323e.
The rovibrational energy-level structures of BaH and BaD in their XΣ electronic ground state have been characterised by pulsed-field-ionisation zero-kinetic-energy photoelectron spectroscopy following resonance-enhanced (1 + 1') two-photon excitation from the BaH/BaD X Σ ground state the E Π (' = 0, 1) intermediate levels. A full set of rovibrational molecular constants for the BaH and BaD ground states has been derived for the first time and the adiabatic ionisation energies of BaH and BaD were determined to be 38 679.96(20) and 38 652.69(20) cm, respectively. Photoelectron spectra recorded E-state levels of selected rovibronic parity exhibit pronounced intensity alternations of transitions to rotational states of the cations with even- and odd-valued rotational-angular-momentum quantum number . This observation is interpreted by invoking dominant contributions of even- photoelectron partial waves in the photoionisation of the E Π (' = 0, 1) intermediate states of barium hydride. The lowest pure-rotational transition frequencies of BaH and BaD are derived from the photoelectron spectra which may help the detection of BaH in the microwave and millimetre-wave ranges.
通过从BaH/BaD的XΣ基态到EΠ（′ = 0, 1）中间能级的共振增强（1 + 1′）双光子激发后的脉冲场电离零动能光电子能谱，对处于XΣ电子基态的BaH和BaD的振转能级结构进行了表征。首次推导得到了BaH和BaD基态的全套振转分子常数，并且确定BaH和BaD的绝热电离能分别为38 679.96(20)和38 652.69(20) cm⁻¹。记录的具有选定振转宇称的E态能级的光电子能谱显示，向具有偶数和奇数转动角动量量子数J的阳离子转动态跃迁的强度有明显的交替变化。通过调用氢化钡EΠ（′ = 0, 1）中间态光电离中偶数ℓ光电子分波的主要贡献来解释这一观察结果。从光电子能谱中推导得到了BaH和BaD的最低纯转动跃迁频率，这可能有助于在微波和毫米波范围内检测BaH。
