화학공학소재연구정보센터
Journal of the American Chemical Society, Vol.136, No.9, 3589-3596, 2014
The Negative Ion Photoelectron Spectrum of meta-Benzoquinone Radical Anion (MBQ(center dot-)): A Joint Experimental and Computational Study
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 +/- 0.010 eV. Single-point, CASPT2/aug-cc-pVTZ//CASPT2/aug-cc-pVDZ calculations predict accurately the positions of the 0-0 bands in the NIPE spectrum for formation of the four lowest electronic states of neutral MBQ from the (2)A(2) state of MBQ(center dot-). In addition, the Franck-Condon 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(center dot-) allows the assignment of B-3(2) as the ground state of MBQ, followed by the B-1(2) and (1)A(1) electronic states, respectively 9.0 +/- 0.2 and 16.6 +/- 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)