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Ab initio calculations on PO2 and anharmonic Franck-Condon simulations of its single-vibrational-level emission spectra

机译：PO2的从头算计算及其单振动级发射光谱的非谐Franck-Condon模拟

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Geometry optimization and harmonic vibrational frequency calculations were carried out on some low-lying electronic states of PO2 at the CIS, CASSCF, MP2, and RCCSD(T) levels with various standard basis sets of at least valence triple-ζ quality. Relative electronic energies, including vertical excitation energies from the X̃2A1 state {with the electronic configuration of ...(7a1)2(8a1)1} and Te values, were computed at the RCCSD(T) and CASSCF/MRCI levels with basis sets of up to aug-cc-pVQZ quality. These computed results, particularly the computed Te values, suggest that the upper electronic state of the laser induced fluorescence (LIF) and single-vibrational-level (SVL) emission spectra of PO2 reported recently by Lei et al. [J. Phys. Chem. A 2001, 105, 7828] is the 22A1 state of PO2 {with the electronic configuration of ...(7a1)1(8a1)2}. RCCSD(T)/ aug-cc-pVQZ and CASSCF/MRCI/aug-cc-pVQZ(no g) energy scans were carried out on the X̃2A1 and 22A1 states of PO2, respectively, in the symmetric stretching and bending coordinates. Franck-Condon factors (FCFs) between the two states, which allow for the Duschinsky and anharmonic effects, were calculated employing the potential energy functions obtained from the ab initio scans. Comparison between the simulated spectra based on the computed FCFs and observed SVL emission spectra led to reassignments of the vibrational designations of the emitting SVLs in the upper state. On the basis of the excellent agreement between the simulated spectra for the revised SVLs and the observed emission spectra, the electronic transition involved in the LIF and SVL emission spectra reported by Lei et al. is confirmed to be 22A2-X̃2A1 of PO2. Following the revised vibrational assignments of the upper electronic state in the SVL emissions, the vibrational assignments of the LIF excitation bands given by Lei et al. are revised and a revised T0 value of 30660 cm-1 is estimated for the 22A1 state of PO2. In addition, employing the iterative Franck-Condon analysis (IFCA) procedure in the simulation of the SVL emission spectra, the equilibrium geometry of the 22A1 state of PO2 is derived for the first time (re = 1.560 Å; θe = 116.5°).
机译：对PO2在CIS，CASSCF，MP2和RCCSD（T）级别的一些低电子态进行了几何优化和谐波振动频率计算，并具有至少价三重ζ质量的各种标准基础集。相对电子能量，包括来自X̃2A1状态的垂直激发能量（具有...（7a1）2（8a1）1的电子配置）和Te值，在RCCSD（T）和CASSCF / MRCI级别上使用基集进行计算最高可达aug-cc-pVQZ质量。这些计算结果，特别是计算出的Te值，表明Lei等人最近报道的PO2的激光诱导荧光（LIF）和单振动能级（SVL）发射光谱的较高电子状态。 [J.物理化学A 2001、105、7828]是PO2的22A1状态{具有...（7a1）1（8a1）2 ...的电子配置}。在对称的拉伸和弯曲坐标下，分别在PO2的X̃2A1和22A1状态下进行RCCSD（T）/ aug-cc-pVQZ和CASSCF / MRCI / aug-cc-pVQZ（no g）能量扫描。利用从头算扫描获得的势能函数，计算了允许Duschinsky和非谐效应的两个状态之间的弗兰克-康登因子（FCF）。基于所计算的FCF的模拟光谱与观察到的SVL发射光谱之间的比较导致重新分配了处于较高状态的发射SVL的振动名称。基于修正后的SVL的模拟光谱与观察到的发射光谱之间的极好的一致性，Lei等人报道了参与LIF和SVL发射光谱的电子跃迁。确认为PO2的22A2-X̃2A1。根据SVL发射中上电子态的修正振动分配，Lei等人给出了LIF激发带的振动分配。进行了修订，对于PO2的22A1状态，修订后的T0值为30660 cm-1。此外，在SVL发射光谱的模拟中采用迭代Franck-Condon分析（IFCA）程序，首次得出PO2的22A1状态的平衡几何形状（re = 1.560Å；θe= 116.5°）。

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