Impact of the dipole-moment representation on the intensity of high overtones
Impact of the dipole-moment representation on the intensity of high overtones
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偶极矩表示对高泛音强度的影响
DOI：
10.1016/j.jms.2016.06.013
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发表时间：
2016
影响因子：
1.4
通讯作者：
I. Gordon
中科院分区：
文献类型：
--
作者：
E. S. Medvedev;V. Meshkov;A. Stolyarov;V. Ushakov;I. Gordon
计算振转跃迁的强度对于从给定的振动态到解离极限的所有上态的跃迁特别具有挑战性，因为它们的几率随着振动量子数的变化Δn的增加而指数减小。可用于低Δn值的实验强度可以被各种模型很好地再现，但在预测未观测到的高泛音跃迁的强度时，这些模型可能会有很大的分歧，这种分歧随着泛音数目的增加而迅速增加。本文研究了偶极矩函数(DMF)表示对CO分子高泛音强度模拟的影响。我们测试了不同的DMF形式，包括结合三次样条插值的逐点表示、幂和三角展开以及Padé逼近。数值计算采用Coxon和Hajigorgiou(2004)的高精度经验势能函数(PEF)，采用四重精度算法。根据正常强度分布定律(NIDL)，大多数计算的强度在整个转变范围内都会下降(Medvedev，2012)。对于给定的PEF，NIDL趋势线的斜率在不同的解析DMF之间变化不大，因为斜率基本上与PEF有关。在NIDL的基础上，可以确定模拟强度下降到离解极限的极限。我们认为，用解析函数表示的DMF对于所有的跃迁都能产生最佳结果。逐点函数(特别是通过传统的三次样条法进行内插)导致了高Δn跃迁时强度的非物理平坦，对于CO，Δn>；7。
Calculating intensities of ro-vibrational transitions is particularly challenging for transitions from a given vibrational state to all upper states up to the dissociation limit because their probabilities decrease exponentially with increasing Δ n, the change in the vibrational quantum number. The experimental intensities available for low-Δ n values are well reproduced by a variety of models but the models can greatly diverge in predicting the intensities of unobserved high-overtone transitions, the divergence rapidly increasing with the overtone number. In this paper, we investigate the impact of the dipole-moment function (DMF) representation on the high-overtone intensity simulation of the CO molecule. We tested various DMF forms including pointwise representation combined with cubic-spline interpolation, power and trigonometric expansions, and Padé approximants. Numerical calculations were performed with the highly accurate empirical potential-energy function (PEF) of Coxon and Hajigeorgiou (2004) using quadruple-precision arithmetic. Most calculated intensities fall off in the entire range of transitions according to the Normal Intensity Distribution Law (NIDL)(Medvedev, 2012). The slope of the NIDL trend line varies little between different analytical DMFs for a given PEF since the slope is basically associated with the PEF. Based on the NIDL, the limits within which the simulated intensities fall off up to the dissociation limit can be established. We claim that DMFs represented by analytical functions yield best results for all transitions. The pointwise functions (interpolated, in particular, by the conventional cubic splines) result in an unphysical flattening of the intensities at high-Δ n transitions, Δ n> 7 for CO.