The Negative Ion Photoelectron Spectrum of meta-Benzoquinone Radical Anion (MBQ鈥⑩€?/sup>): A Joint Experimental and Computational Study

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• 作者：Bo Chen ; David A. Hrovat ; S. H. M. Deng ; Jian Zhang ; Xue-Bin Wang ; Weston Thatcher Borden
• 刊名：Journal of the American Chemical Society
• 出版年：2014
• 出版时间：March 5, 2014
• 年：2014
• 卷：136
• 期：9
• 页码：3589-3596
• 全文大小：318K
• 年卷期：v.136,no.9(March 5, 2014)
• ISSN：1520-5126

文摘

Negative ion photoelectron (NIPE) spectra of the radical anion of meta-benzoquinone (MBQ, m-OC₆H₄O) have been obtained at 20 K, using both 355 and 266 nm lasers for electron photodetachment. The spectra show well-resolved peaks and complex spectral patterns. The electron affinity of MBQ is determined from the first resolved peak to be 2.875 卤 0.010 eV. Single-point, CASPT2/aug-cc-pVTZ//CASPT2/aug-cc-pVDZ calculations predict accurately the positions of the 0鈥? bands in the NIPE spectrum for formation of the four lowest electronic states of neutral MBQ from the ²A₂ state of MBQ^{鈥⑩€?/sup>. In addition, the Franck鈥揅ondon factors that are computed from the CASPT2/aug-cc-pVDZ optimized geometries, vibrational frequencies, and normal mode vectors, successfully simulate the intensities and frequencies of the vibrational peaks in the NIPE spectrum that are associated with each of these electronic states. The successful simulation of the NIPE spectrum of MBQ鈥⑩€?/sup> allows the assignment of 3B₂ as the ground state of MBQ, followed by the 1B₂ and 1A₁ electronic states, respectively 9.0 卤 0.2 and 16.6 卤 0.2 kcal/mol higher in energy than the triplet. These experimental energy differences are in good agreement with the calculated values of 9.7 and 15.7 kcal/mol. The relative energies of these two singlet states in MBQ confirm the previous prediction that their relative energies would be reversed from those in meta-benzoquinodimethane (MBQDM, m-CH₂C₆H₄CH₂).}