Calculated and Empirical Values of Vibronic Transition Dipole Moments of Reactive Chemical Intermediates for Determination of Concentrations
Calculated and Empirical Values of Vibronic Transition Dipole Moments of Reactive Chemical Intermediates for Determination of Concentrations
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用于测定浓度的反应性化学中间体的电子振动偶极矩的计算值和经验值
DOI：
10.1021/acs.jpca.3c01584
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发表时间：
2023
期刊：
影响因子：
--
通讯作者：
Stanton, John F.
中科院分区：
文献类型：
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作者：
Jones, Ian W.;Bersson, Jonathan S.;Liu, Jinjun;Sharma, Ketan;Vasilyev, Oleg A.;Miller, Terry A.;Stanton, John F.
长期以来，吸收光谱一直被认为是一种进行分子浓度测量的技术，近年来随着新技术的出现，如腔衰荡光谱的出现，吸收光谱的灵敏度得到了提高。要应用该方法，必须有一个已知的分子吸收横截面为感兴趣的物种，这通常是通过测量已知浓度的标准样品得到的。然而，这种方法失败，如果该物种是高度反应性的，和间接的手段，以获得截面必须采用。ho2和烷基过氧自由基是反应物质的例子，其吸收截面已被报道。这项工作探索和描述了这些过氧自由基的另一种方法的细节，该方法使用量子化学方法计算过渡偶极矩，以获得这些横截面，横截面取决于其平方。同样，给出了从ho2的近红外Ã-X /电子谱中实验测量的单个振动谱线的横截面和烷基（甲基、乙基和乙酰基）过氧自由基相应电子跃迁的旋转轮廓峰中获得跃迁矩的详细信息。对于烷基过氧自由基，两种方法的过渡矩一致性较好，约为20%。然而，令人惊讶的是，ho2自由基的一致性明显较差，约为40%。讨论了这种分歧的可能原因。
Absorption spectroscopy has long been known as a technique for making molecular concentration measurements and has received enhanced visibility in recent years with the advent of new techniques, like cavity ring-down spectroscopy, that have increased its sensitivity. To apply the method, it is necessary to have a known molecular absorption cross section for the species of interest, which typically is obtained by measurements of a standard sample of known concentration. However, this method fails if the species is highly reactive, and indirect means for attaining the cross section must be employed. The HO2and alkyl peroxy radicals are examples of reactive species for which absorption cross sections have been reported. This work explores and describes for these peroxy radicals the details of an alternative approach for obtaining these cross sections using quantum chemistry methods for the calculation of the transition dipole moment upon whose square the cross section depends. Likewise, details are given for obtaining the transition moment from the experimentally measured cross sections of individual rovibronic lines in the near-IR ÖX̃ electronic spectrum of HO2and the peaks of the rotational contours in the corresponding electronic transitions for the alkyl (methyl, ethyl, and acetyl) peroxy radicals. In the case of the alkyl peroxy radicals, good agreement for the transition moments, ≈20%, is found between the two methods. However, rather surprisingly, the agreement is significantly poorer, ≈40%, for the HO2radical. Possible reasons for this disagreement are discussed.