Pump-probe near edge X-ray absorption fine structure (PP-NEXAFS) spectra of molecules offer insight into valence-excited states, even if optically dark. In PP-NEXAFS spectroscopy, the molecule is “pumped” by UV or visible light enforcing a valence excitation, followed by an X-ray “probe” exciting core electrons into (now) partially empty valence orbitals. Calculations of PP-NEXAFS have so far been done by costly, correlated wavefunction methods which are not easily applicable to medium-sized or large molecules. Here we propose an efficient, first principles method based on density functional theory in combination with the transition potential and ΔSCF methodology (TP-DFT/ΔSCF) to compute molecular ground state and PP-NEXAFS spectra. We apply the method to n → π^* pump/O-K-edge NEXAFS probe spectroscopy of thymine (for which both experimental and other theoretical data exist) and to n → π^* or π → π^* pump/N-K-edge NEXAFS probe spectroscopies of trans- and cis-azobenzene.

中文翻译：

---

分子泵浦探针NEXAFS谱的一种有效的第一原理方法：在胸腺嘧啶和偶氮苯中的应用

分子的近边缘X射线吸收精细结构（PP-NEXAFS）光谱的泵浦探针可洞悉价态，即使在光学上较暗。在PP-NEXAFS光谱学中，该分子被紫外线或可见光“激发”，强制进行化合价激发，然后通过X射线“探测”将核电子激发到（现在）部分为空的化合价轨道中。到目前为止，PP-NEXAFS的计算是通过昂贵的相关波函数方法完成的，这些方法不易应用于中型或大分子。在这里，我们提出一种基于密度泛函理论，结合跃迁势和ΔSCF方法（TP-DFT /ΔSCF）的高效第一原理方法，以计算分子基态和PP-NEXAFS光谱。我们将该方法应用于n → π^*胸腺嘧啶（对于该实验和其他理论数据存在）和泵/ OK-边缘NEXAFS探测光谱Ñ →交通π ^*或π →交通π ^*泵/ NK-边缘NEXAFS探测的光谱反式-和顺-azobenzene。