Laboratory for Optical Physics and Engineering, Department of Electrical and Computer Engineering, University of Illinois, Urbana, Illinois 61801, United States.
Department of Engineering and Physics, Abilene Christian University, Abilene, Texas 79699, United States.
J Phys Chem A. 2023 Apr 27;127(16):3675-3683. doi: 10.1021/acs.jpca.2c07274. Epub 2023 Apr 12.
Interatomic potentials for the BΣ states of CsAr, CsXe, and RbXe have been determined through comparisons of experimental B ← X absorption spectra for alkali vapor-rare gas mixtures with calculations of the Franck-Condon factors (FCFs) associated with free-free transitions of thermal atomic pairs. Simulations of optical transitions of alkali-rare gas atomic pairs between the thermal and vibrational continua of the XΣ and BΣ states of the molecule, responsible for the blue satellites of the Cs and Rb D resonance lines in a rare gas background, require the incorporation of ground-state values above ∼400 into the FCF calculations and proper normalization of the free-particle wave functions. Absorption spectra computed on the basis of several X and B state interatomic potentials available in the literature were found to be sensitive to the height of the BΣ state barrier, as well as the XΣ state repulsive wall contour and the location of the van der Waals minimum. Other spectral simulations entailed iterative modifications to a selected BΣ interatomic potential, again coupled with comparison to experimental B ← X spectra. Comparisons of calculated spectra with experiment yield a CsXe BΣ potential, for example, exhibiting a barrier height of 76 cm at 5.2 Å and yet is nearly flat at smaller values of internuclear separation (). The latter contrasts with previous theoretical calculations of () in the vicinity of the barrier maximum. For the CsAr molecule, the BΣ barrier height was found to be 221 cm, which is within 3% of the value determined from pseudopotential calculations incorporating the spin-orbit effect. Reproducing Cs-rare gas experimental absorption spectra also requires the existence of a broad, shallow potential well lying beyond the BΣ barrier that, for CsAr, has a dissociation energy ( ∼ 24 cm) a factor of 3 larger than values predicted by theory. Similar results are obtained for the RbXe and CsXe complexes.
通过比较碱蒸气-稀有气体混合物的实验 B ← X 吸收光谱与自由-自由跃迁的 Franck-Condon 因子 (FCF) 的计算，确定了 CsAr、CsXe 和 RbXe 的 BΣ 态的原子间势。负责 Cs 和 Rb D 共振线在稀有气体背景下的蓝边卫星的碱-稀有气体原子对在 XΣ 和 BΣ 态分子的热和振动连续体之间的光学跃迁的模拟，需要将基态值以上 ∼400 纳入 FCF 计算中，并对自由粒子波函数进行适当的归一化。根据文献中提供的几种 X 和 B 态原子间势计算出的吸收光谱，发现其对 BΣ 态势垒的高度、XΣ 态排斥壁轮廓和范德华最小值的位置非常敏感。其他光谱模拟需要对选定的 BΣ 原子间势进行迭代修改，同时与实验 B ← X 光谱进行比较。例如，与实验相比，计算出的光谱与 CsXe BΣ 势的比较，表现出 5.2 Å 时 76 cm 的势垒高度，但在核间分离较小的值（）时几乎是平坦的。这与以前在势垒最大值附近对（）的理论计算形成对比。对于 CsAr 分子，发现 BΣ 势垒高度为 221 cm，这与包含自旋轨道效应的赝势计算确定的值相差 3%。重现 Cs-稀有气体实验吸收光谱还需要存在一个宽而浅的势阱，该势阱位于 BΣ 势垒之外，对于 CsAr，其离解能（ ∼ 24 cm）比理论预测的值大 3 倍。对于 RbXe 和 CsXe 配合物，也得到了类似的结果。
