You Hyun Sik, Kim Junggil, Han Songhee, Ahn Doo-Sik, Lim Jean Sun, Kim Sang Kyu
Department of Chemistry, KAIST , Daejeon 34141, Republic of Korea.
J Phys Chem A. 2018 Feb 8;122(5):1194-1199. doi: 10.1021/acs.jpca.7b10431. Epub 2018 Jan 24.
Conformational isomers of hydroquinone and their 1:1 clusters with water have been spatially separated using a Stark deflector in a supersonic jet. trans-Hydroquinone (HyQ) conformer with zero dipole moment is little influenced by inhomogeneous electric fields, whereas cis conformer with nonzero dipole moment (2.38 D) is significantly deflected from the molecular beam axis into the direction along which the strong field gradient is applied. Resonant two photon ionization carried out by shifting the laser position perpendicular to the molecular beam axis after the Stark deflector then gives an exclusive S-S excitation spectrum of the cis conformer only, making possible immaculate conformer-specific spectroscopy and dynamics. As the spatial separation is apparently proportional to the effective dipole moment strength, conformational assignment could be absolute in the Stark deflector, which contrasts with the hole-burning spectroscopic technique where identification of a conformational isomer is intrinsically not unambiguous. trans- and cis-HyQ-HO clusters have also been spatially separated according to their distinct effective dipole moment strengths to give absolute spectroscopic identification of each cluster isomer, nailing down the otherwise disputable conformational assignment. This is the first report for the spatial separation of conformational cluster isomers.
对苯二酚的构象异构体及其与水的1:1团簇已在超声速射流中使用斯塔克偏转器进行了空间分离。偶极矩为零的反式对苯二酚（HyQ）构象异构体受非均匀电场的影响很小，而偶极矩非零（2.38 D）的顺式构象异构体则从分子束轴显著偏向施加强场梯度的方向。在斯塔克偏转器之后，通过将激光位置垂直于分子束轴移动来进行共振双光子电离，然后仅给出顺式构象异构体的专属S-S激发光谱，从而实现完美的构象异构体特异性光谱学和动力学研究。由于空间分离显然与有效偶极矩强度成正比，因此在斯塔克偏转器中构象归属可以是绝对的，这与空穴烧蚀光谱技术形成对比，在空穴烧蚀光谱技术中，构象异构体的鉴定本质上并不明确。反式和顺式HyQ-H₂O团簇也根据其不同的有效偶极矩强度进行了空间分离，以对每个团簇异构体进行绝对光谱鉴定，确定了否则存在争议的构象归属。这是关于构象团簇异构体空间分离的首次报道。
