Yuan-Pin Chang

Specific Chemical Reactivities of Spatially Separated 3-Aminophenol Conformers with Cold Ca+ Ions

Reactive Conformations Most molecules manifest a fair amount of flexibility at room temperature, in particular through interconversion of rotational conformers—structures that differ by the relative orientation of groups on either side of a single covalent bond. Chang et al. (p. 98; see the Perspective by Heaven) devised a method to explore the comparative reactivities of different conformers. A mixture of the conformers was prepared in a molecular beam cold enough to preclude interconversion; then an electric field was used to push the different conformers apart, spatially resolving subsequent collisional interactions with a target of trapped ions. A molecular beam technique measures the different reactivities of a compound’s distinct rotational conformations. [Also see Perspective by Heaven] Many molecules exhibit multiple rotational isomers (conformers) that interconvert thermally and are difficult to isolate. Consequently, a precise characterization of their role in chemical reactions has proven challenging. We have probed the reactivity of specific conformers by using an experimental technique based on their spatial separation in a molecular beam by electrostatic deflection. The separated conformers react with a target of Coulomb-crystallized ions in a trap. In the reaction of Ca+ with 3-aminophenol, we find a twofold larger rate constant for the cis compared with the trans conformer (differentiated by the O–H bond orientation). This result is explained by conformer-specific differences in the long-range ion-molecule interaction potentials. Our approach demonstrates the possibility of controlling reactivity through selection of conformational states.

Separating Para and Ortho Water

Water exists as two nuclear-spin isomers, para and ortho, determined by the overall spin of its two hydrogen nuclei. For isolated water molecules, the conversion between these isomers is forbidden and they act as different molecular species. Yet, these species are not readily separated, and no pure para sample has been produced. Accordingly, little is known about their specific physical and chemical properties, conversion mechanisms, or interactions. The production of isolated samples of both spin isomers is demonstrated in pure beams of para and ortho water in their respective absolute ground state. These single-quantum-state samples are ideal targets for unraveling spin-conversion mechanisms, for precision spectroscopy and fundamental symmetry-breaking studies, and for spin-enhanced applications, for example laboratory astrophysics and astrochemistry or hypersensitized NMR experiments.

Spatial separation of state- and size-selected neutral clusters

We demonstrate the spatial separation of the prototypical indole(H

Spatially-controlled complex molecules and their applications

{}_{2}

Spatially separated polar samples of the cis and trans conformers of 3-fluorophenol

O) clusters from the various species present in the supersonic expansion of mixtures of indole and water. The major molecular constituents of the resulting molecular beam are H

Spatial Separation of Molecular Conformers and Clusters

{}_{2}

CMIstark: Python package for the Stark-effect calculation and symmetry classification of linear, symmetric and asymmetric top wavefunctions in dc electric fields

O, indole, indole(H

Chemical reactions of conformationally selected 3-aminophenol molecules in a beam with Coulomb-crystallized Ca+ ions

{}_{2}

Trennung von para‐und ortho‐Wasser

O), and indole(H

Chemical reactions of conformationally selected molecules in a beam with Coulomb-crystallized ions

{}_{2}