Bregnhøj Mikkel, Ogilby Peter R
Center for Oxygen Microscopy and Imaging, Department of Chemistry, Aarhus University , Langelandsgade 140, Aarhus 8000, Denmark.
J Phys Chem A. 2015 Sep 3;119(35):9236-43. doi: 10.1021/acs.jpca.5b05131. Epub 2015 Jul 16.
Radiative transitions between the three lowest-lying electronic states of molecular oxygen have long provided a model to study how collision-dependent perturbations influence forbidden processes. In an isolated oxygen molecule, transitions between the O2(X(3)Σg(-)), O2(a(1)Δg), and O2(b(1)Σg(+)) states are forbidden as electric-dipole processes. For oxygen dissolved in organic solvents, the probabilities of radiative transitions between these states increase appreciably. Attempts to interpret solvent-dependent changes in the radiative rate constants have principally relied on O2(b(1)Σg(+)) and O2(a(1)Δg) emission experiments. However, the dominant nonradiative deactivation channels of O2(b(1)Σg(+)) make it difficult to quantify solvent effects on the O2(b(1)Σg(+)) → O2(a(1)Δg) radiative process. Thus, an appreciable amount of important information has heretofore not been available. In the present study, we examined the effect of 17 common organic solvents on the O2(a(1)Δg) → O2(b(1)Σg(+)) absorption transition at ∼5200 cm(-1) (i.e., ∼1925 nm). The solvent-dependent absorption coefficients at the band maximum, εmax, range from 5 to 50 M(-1) cm(-1) and correlate reasonably well with the solvent refractive index; εmax is largest in solvents with the largest refractive index. This observation is consistent with a model in which oxygen is perturbed to a greater extent by solvents with a large electronic polarizability. Through the Strickler-Berg equation, we also used these absorption data to obtain the radiative rate constant for the O2(b(1)Σg(+)) → O2(a(1)Δg) transition, and the results are consistent with a model in which the O2(a(1)Δg) → O2(X(3)Σg(-)) transition is said to steal intensity from the O2(b(1)Σg(+)) → O2(a(1)Δg) transition.
长期以来，分子氧的三个最低电子态之间的辐射跃迁为研究碰撞依赖的微扰如何影响禁戒过程提供了一个模型。在孤立的氧分子中，O₂(X³Σg⁻)、O₂(a¹Δg)和O₂(b¹Σg⁺)态之间的跃迁作为电偶极过程是禁戒的。对于溶解在有机溶剂中的氧，这些态之间辐射跃迁的概率会显著增加。解释辐射速率常数中溶剂依赖性变化的尝试主要依赖于O₂(b¹Σg⁺)和O₂(a¹Δg)发射实验。然而，O₂(b¹Σg⁺)的主要非辐射失活通道使得难以量化溶剂对O₂(b¹Σg⁺)→O₂(a¹Δg)辐射过程的影响。因此，迄今为止还没有大量重要信息可用。在本研究中，我们研究了17种常见有机溶剂对O₂(a¹Δg)→O₂(b¹Σg⁺)在5200 cm⁻¹（即1925 nm）处吸收跃迁的影响。在谱带最大值处的溶剂依赖性吸收系数εmax范围为5至50 M⁻¹ cm⁻¹，并且与溶剂折射率有合理的良好相关性；εmax在折射率最大的溶剂中最大。这一观察结果与一个模型一致，在该模型中，氧受到具有大电子极化率的溶剂的更大程度的微扰。通过斯特里克勒 - 伯格方程，我们还利用这些吸收数据获得了O₂(b¹Σg⁺)→O₂(a¹Δg)跃迁的辐射速率常数，结果与一个模型一致，在该模型中，O₂(a¹Δg)→O₂(X³Σg⁻)跃迁据说从O₂(b¹Σg⁺)→O₂(a¹Δg)跃迁中窃取了强度。
