The near-edge X-ray absorption fine structure (NEXAFS) and X-ray photoelectron (XP) spectra of gas-phase 2,8-bis(diphenylphosphoryl)dibenzo[b,d]thiophene (PPT) and triphenylphosphine oxide (TPPO) have been measured at the S and P L_II,III-edge regions. The time-dependent density functional theory (TDDFT) based on the relativistic two-component zeroth-order regular approximation approach has been used to provide an assignment of the experimental spectra, giving the contribution of the spin–orbit splitting and of the molecular-field splitting to the sulfur and phosphor binding energies. Computed XP and NEXAFS spectra agree well with the experimental measurements. In going from dibenzothiophene and TPPO to PPT, the nature of the most intense S 2p and P 2p NEXAFS features are preserved; this trend suggests that the electronic and geometric behaviors of the S and P atoms in the two building block moieties are conserved in the more complex system of PPT. This work enables us to shed some light onto the structure of the P–O bond, a still highly debated topic in the chemical literature. Since the S 2p and P 2p NEXAFS intensities provide specific information on the higher-lying localized σ*(C–S) and σ*(P–O) virtual MOs, we have concluded that P 3d AOs are not involved in the formation of the P–O bond. Moreover, the results support the mechanism of negative hyperconjugation, by showing that transitions toward σ*(P–O) states occur at lower energies with respect to those toward π*(P–O) states.

中文翻译：

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PPT双极材料及其构成部分的S 2p和P 2p核心能级谱

气相2,8-双（二​​苯基磷酰基）二苯并[ b，d ]噻吩（PPT）和三苯基氧化膦（TPPO）的近边缘X射线吸收精细结构（NEXAFS）和X射线光电子能谱在S和PL _{II，III处测量}边缘区域。基于相对论两分量零阶正则逼近方法的时变密度泛函理论（TDDFT）已用于提供实验光谱的分配，从而给出了自旋轨道分裂和分子场的贡献分裂成硫和磷的结合能。计算的XP和NEXAFS光谱与实验测量结果非常吻合。从二苯并噻吩和TPPO过渡到PPT时，保留了最强烈的S 2p和P 2p NEXAFS特征的性质；这一趋势表明，在更复杂的PPT系统中，两个构件部分中S和P原子的电子和几何行为均得到保留。这项工作使我们能够阐明P-O键的结构，这在化学文献中仍然是一个备受争议的话题。由于S 2p和P 2p NEXAFS强度提供有关较高位置的局部σ*（CS）和σ*（PO）虚拟MO的特定信息，因此我们得出结论，P 3d AO不参与形成P–O键。此外，结果表明，向σ*（PO）状态的跃迁相对于向π*（PO）状态的跃迁以较低的能量发生，从而支持了负超共轭机理。