Jaquet Ralph
Theoretical Chemistry, Department of Chemistry and Biology, Siegen University, 57068 Siegen, Germany.
J Chem Phys. 2024 Aug 7;161(5). doi: 10.1063/5.0215051.
In this article, significant contributions of non-adiabaticity for the rovibrational bound states up to 25 000 cm-1 and total angular momentum J = 0-20 of H3+ are investigated. A coupled-perturbed full configuration interaction (CP-FCI) treatment is applied to calculate all couplings between electronic states caused by the nuclear motion. These derivative couplings were evaluated up to the second order by means of a perturbation treatment and include all nuclear Cartesian first and second derivatives of the electronic wavefunctions. In particular, the coupling of special derivatives with respect to r and R in the Jacobi coordinate representation is more significant than thought. The perturbation approach is especially optimal for the treatment of weak non-adiabaticity in case of rovibrational energies in H3+ and had not been available before for H3+ or other triatomics. Using exclusively Gaussian basis functions for CP-FCI appears to be sufficient, because explicit correlated wavefunctions are already used for all other potential energy contributions. Our work is an extension of earlier non-adiabatic investigations based on first derivative couplings of electronic states that led to the concept of geometry-dependent effective nuclear masses and which needs only a single potential energy surface for the dynamics. The implementation allows us to include all non-adiabatic effects up to the order of O(μ-2), μ being the reduced nuclear mass. Our treatment works for any isotopologue and for the whole potential energy curve or surface. By this treatment, a further reduction in deviations to experimental data for most rovibrational levels to less than 0.1 cm-1 is possible. For the related transition frequencies, 1366 of 1720 known rovibrational transitions in H3+ have deviations less than 0.1 cm-1 without using any empirically adjustable parameters or optimizing the nuclear mass for a specific transition. For many questionable assignments (deviations >0.3 cm-1) of observed transitions in H3+, a new labeling is proposed.
在本文中，研究了非绝热性对H₃⁺高达25000 cm⁻¹的振转束缚态以及总角动量J = 0 - 20的显著贡献。采用耦合微扰全组态相互作用（CP - FCI）方法来计算由核运动引起的电子态之间的所有耦合。这些导数耦合通过微扰处理计算到二阶，包括电子波函数的所有核笛卡尔一阶和二阶导数。特别地，在雅可比坐标表示中，相对于r和R的特殊导数的耦合比预期的更显著。微扰方法对于处理H₃⁺振转能量情况下的弱非绝热性尤为理想，并且此前H₃⁺或其他三原子分子尚未有此方法。对于CP - FCI仅使用高斯基函数似乎就足够了，因为所有其他势能贡献已经使用了显式相关波函数。我们的工作是早期基于电子态一阶导数耦合的非绝热研究的扩展，该研究引出了几何依赖有效核质量的概念，并且动力学只需要一个势能面。该实现方式使我们能够纳入高达O(μ⁻²)阶的所有非绝热效应，μ为约化核质量。我们的处理方法适用于任何同位素分子以及整个势能曲线或曲面。通过这种处理，对于大多数振转能级，与实验数据的偏差有可能进一步降低到小于0.1 cm⁻¹。对于相关的跃迁频率，在不使用任何经验可调参数或针对特定跃迁优化核质量的情况下，H₃⁺中1720个已知振转跃迁中的1366个偏差小于0.1 cm⁻¹。对于H₃⁺中许多观测跃迁的可疑归属（偏差>0.3 cm⁻¹），提出了一种新的标记方法。
