Abstract
We present a unique experimental design that enables the measurement of photoelectron circular dichroism (PECD) from chiral molecules in aqueous solution. The effect is revealed from the intensity difference of photoelectron emission into a backward-scattering angle relative to the photon propagation direction when ionizing with circularly polarized light of different helicity. This leads to asymmetries (normalized intensity differences) that depend on the handedness of the chiral sample and exceed the ones in conventional dichroic mechanisms by orders of magnitude. The asymmetry is largest for photon energies within several electron volts above the ionization threshold. A primary aim is to explore the effect of hydration on PECD. The modular and flexible design of our experimental setup EASI (Electronic structure from Aqueous Solutions and Interfaces) also allows for detection of more common photoelectron angular distributions, requiring distinctively different detection geometries and typically using linearly polarized light. A microjet is used for liquid-sample delivery. We describe EASI's technical features and present two selected experimental results, one based on synchrotron-light measurements and the other performed in the laboratory, using monochromatized He-II α radiation. The former demonstrates the principal effectiveness of PECD detection, illustrated for prototypic gas-phase fenchone. We also discuss the first data from liquid fenchone. In the second example, we present valence photoelectron spectra from liquid water and NaI aqueous solution, here obtained from a planar-surface microjet (flatjet). This new development features a more favorable symmetry for angle-dependent photoelectron measurements.
Highlights
General considerationsPhotoelectron spectroscopy (PES) studies from liquids and from water and aqueous solutions, mostly in conjunction with a liquid microjet, have contributed tremendously to our current understanding of the aqueous-phase electronic structure
We have presented a unique experimental setup, EASI, with all major components, that enables photoelectron circular dichroism (PECD) and regular photoelectron angular distribution (PAD) measurements, associated with the chiral b1 and non-chiral b2 anisotropy parameters, respectively, from liquid microjets of solutions
EASI’s principal configurations—one for PECD and three for regular PAD measurements—and how transformation between those configurations is accomplished time-effectively and with rather little effort have been described in detail
Summary
Photoelectron spectroscopy (PES) studies from liquids and from water and aqueous solutions, mostly in conjunction with a liquid microjet, have contributed tremendously to our current understanding of the aqueous-phase electronic structure. Scitation.org/journal/rsi ionized are carefully shielded by a full μ-metal encasement, enabling the detection of photoelectrons and elastically and inelastically scattered electrons down to near-zero-eV kinetic energy with quantitative accuracy, as required for studying any (near) ionizationthreshold phenomena This includes the measurement of the low-energy cutoff and low-energy tail in a water or aqueous-solution PE spectrum.. If linear polarization with a variable orientation of the polarization ellipse is available, any detection angle within 0○–90○ can be realized for any of the three geometries, and photoelectron angular distributions (PADs) can be fully mapped out allowing for a determination of the common (dipolar) anisotropy parameter, β, from aqueous solution of both the water solvent and solute This parameter can reveal hydrogenbonding-induced orbital structural changes at the solution–vacuum interface and provides insight into the molecular structure at such interfaces.. It is useful though to first review the aforementioned anisotropy parameters, which are relevant for PAD and PECD experiments
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
