Spatial Isolation of Conformational Isomers of Hydroquinone and Its Water Cluster Using the Stark Deflector

Abstract

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.

A novel crossed-molecular-beam experiment for investigating reactions of state- and conformationally selected strong-field-seeking molecules

“…Besides the investigation of state-specific reactions demonstrated here, the novel CMB setup is also suited for studies of conformational effects in reactions of complex molecules under single-collision conditions, in analogy to our previous studies on conformationally selected ion-molecule reactions. 69,70 As conformers of a wide range of molecules have already been spatially separated with the present method, 63,66,67,69,70,94 a variety of reactions is amenable to the present approach. The ability of the electrostatic deflector to select different sizes of molecular clusters 59,94,95 would allow for reactions with even more complex reactants.…”

“…69,70 As conformers of a wide range of molecules have already been spatially separated with the present method, 63,66,67,69,70,94 a variety of reactions is amenable to the present approach. The ability of the electrostatic deflector to select different sizes of molecular clusters 59,94,95 would allow for reactions with even more complex reactants. Moreover, the discharge source developed for the present setup is also capable of producing high-density molecular beams of free radicals 76 paving the way for the investigation of state-and conformer-specific effects in reactions with these species in the present setup.…”

A novel crossed-molecular-beam experiment for investigating reactions of state- and conformationally selected strong-field-seeking molecules

“…69,70 As conformers of a wide range of molecules have already been spatially separated with the present method, 63,66,67,69,70,94 a variety of reactions is amenable to the present approach. The ability of the electrostatic deflector to select different sizes of molecular clusters 59,94,95 would allow for reactions with even more complex reactants. Moreover, the discharge source developed for the present setup is also capable of producing high-density molecular beams of free radicals 76 paving the way for the investigation of state-and conformer-specific effects in reactions with these species in the present setup.…”

Tunneling dynamics dictated by the multidimensional conical intersection seam in the πσ*‐mediated photochemistry of heteroaromatic molecules

“…For hydroquinone, the S 1 lifetime turns out to be not conformer‐specific, giving τ ~ 2.8 ns for both trans and cis conformers. Spectroscopic identification of trans and cis conformers of hydroquinone and their water clusters had been well established by the recent Stark deflection experiment, 169 where the differences in dipole moments of different conformers have been utilized for the spatial deflection in the strong electric field, giving the unambiguous identification of the structural isomers of hydroquinone and its water clusters. The S 1 decay is facilitated by the water clustering for both trans and cis of hydroquinone, giving τ ~ 2.27 or 1.92 ns, respectively, which is attributed to the electron‐withdrawing effect of hydrogen‐bonded water on the OH moiety in the para position with respect to the free OH moiety undergoing the H‐atom detachment via tunneling.…”