Chakraborty S, Misra P, Wategaonkar S
Department of Chemical Sciences, Tata Institute of Fundamental Research, Mumbai-400005, India.
J Chem Phys. 2007 Sep 28;127(12):124317. doi: 10.1063/1.2780158.
Zero kinetic energy (ZEKE) photoelectron spectroscopy of the hydroquinone-water (HQW) complex was carried out to characterize its S(1)-S(0) resonantly enhanced multiphoton ionization (REMPI) spectrum in terms of the cis and trans conformers. The ZEKE spectra of the hydroquinone isomers show differences in the Franck-Condon (FC) activity of a few ring modes, viz., modes 15, 9b, and 6b, due to the different symmetries of the two isomers. These modes were used as a "diagnostic tool" to carry out the categorical assignment of the REMPI spectrum of the HQW complex. It was found that the FC activity of these diagnostic modes in the cationic ground state (D(0)) of the water complex is similar as that of the monomer. The two lowest energy transitions in the REMPI spectrum of the water complex, 33,175 and 33,209 cm(-1), were reassigned as the band origins of the cis and trans hydroquinone-water complexes, which is opposite of the previous assignment. The intermolecular stretching mode (sigma) of the complex shows a long progression, up to v(')=4, in the cationic ground state and is strongly coupled to other observed ring modes. The Franck-Condon factors for different members in the progression were calculated using the potential energy surfaces computed ab initio. These agree well with the observed intensity patterns in the progression. The ionization potential of the trans and cis complexes was determined to be 60,071+/-4 and 60,024+/-4 cm(-1), respectively.
对苯二酚 - 水（HQW）配合物进行了零动能（ZEKE）光电子能谱分析，以根据顺式和反式构象表征其S(1)-S(0)共振增强多光子电离（REMPI）光谱。对苯二酚异构体的ZEKE光谱显示，由于两种异构体的对称性不同，一些环模式（即模式15、9b和6b）的弗兰克 - 康登（FC）活性存在差异。这些模式被用作“诊断工具”，对HQW配合物的REMPI光谱进行分类归属。结果发现，这些诊断模式在水配合物阳离子基态（D(0)）中的FC活性与单体的相似。水配合物REMPI光谱中两个最低能量跃迁，即33,175和33,209 cm⁻¹，被重新指定为顺式和反式对苯二酚 - 水配合物的带起源，这与之前的归属相反。配合物的分子间伸缩模式（σ）在阳离子基态显示出长达v(')=4的长进展，并且与其他观察到的环模式强烈耦合。使用从头算计算的势能面计算了进展中不同成员的弗兰克 - 康登因子。这些与进展中观察到的强度模式吻合良好。反式和顺式配合物的电离势分别确定为60,071±4和60,024±4 cm⁻¹。
