Chiral signatures in angle-resolved valence photoelectron spectroscopy of pure glycidol enantiomers.
12 Mar 2008-Physical Chemistry Chemical Physics (The Royal Society of Chemistry)-Vol. 10, Iss: 12, pp 1628-1639
TL;DR: It is found that a nearly quantitative agreement between theory and experiments can be achieved for the ionization of several molecular orbitals, and due to the sensitivity of PECD to molecular conformation this allows us to identify the dominant conformer.
Abstract: Photoionization of the chiral molecule glycidol has been investigated in the valence region Photoelectron circular dichroism (PECD) curves have been obtained at various photon energies by using circularly polarized VUV synchrotron radiation and a velocity map imaging technique to record angle-resolved photoelectron spectra (PES) The measured chiral asymmetries vary dramatically with the photon energy as well as with the ionized orbital, improving the effective orbital resolution of the PECD spectrum with respect to the PES Typical asymmetry factors of 5% are observed, but the peak values measured range up to 15% The experimental results are interpreted by continuum multiple scattering (CMS-Xα) calculations for several thermally accessible glycidol conformers We find that a nearly quantitative agreement between theory and experiments can be achieved for the ionization of several molecular orbitals Owing to the sensitivity of PECD to molecular conformation this allows us to identify the dominant conformer The influence of intramolecular hydrogen bond orbital polarization is found to play a small yet significant role in determining the chiral asymmetry in the electron angular distributions
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TL;DR: The capabilities and the potential of PECD are illustrated with various experimental examples and computational methods that are able to model quantitatively experimental PECD results are introduced, focusing on velocity map coincidence imaging where the momentum distribution of both the electron and the coincident ion is measured.
Abstract: In this Perspective we discuss photoelectron circular dichroism (PECD), a relatively novel technique that can detect chiral molecules with high sensitivity. PECD has an enantiomeric sensitivity of typically 1–10%, which is two to three orders of magnitude larger than that of the widely employed technique of circular dichroism (CD). In PECD a chiral molecule is photoionized with circular polarized light, and the photoelectron angular scattering distribution is detected using particle imaging techniques. We present the general physical principles of photoelectron circular dichroism and we address both single- and multiphoton excitation. PECD has been measured with synchrotron radiation in single-photon ionization as well as, very recently, with femtosecond laser radiation in multiphoton ionization. We discuss the experimental implementation of PECD, focusing on velocity map coincidence imaging where the momentum distribution of both the electron and the coincident ion is measured. The coincident detection of the mass and momentum of the ion adds very powerful mass-correlated information to the PECD measurement of the chiral molecule. We illustrate the capabilities and the potential of PECD with various experimental examples and introduce computational methods that are able to model quantitatively experimental PECD results. We conclude with an outlook on novel developments and (analytical) implementations of PECD that may further broaden the application of PECD for the sensitive detection of chirality in molecules.
159 citations
TL;DR: It is reported that the forward-backward asymmetry in the electron angular distribution, with respect to the photon axis, which is associated with photoelectron circular dichroism can surprisingly reverse direction according to the ion vibrational mode excited.
Abstract: Electron–nuclei coupling accompanying excitation and relaxation processes is a fascinating phenomenon in molecular dynamics. A striking and unexpected example of such coupling is presented here in the context of photoelectron circular dichroism measurements on randomly oriented, chiral methyloxirane molecules, unaffected by any continuum resonance. Here, we report that the forward-backward asymmetry in the electron angular distribution, with respect to the photon axis, which is associated with photoelectron circular dichroism can surprisingly reverse direction according to the ion vibrational mode excited. This vibrational dependence represents a clear breakdown of the usual Franck–Condon assumption, ascribed to the enhanced sensitivity of photoelectron circular dichroism (compared with other observables like cross-sections or the conventional anisotropy parameter-b) to the scattering phase off the chiral molecular potential, inducing a dependence on the nuclear geometry sampled in the photoionization process. Important consequences for the interpretation of such dichroism measurements within analytical contexts are discussed.
122 citations
TL;DR: A photoelectron-photoion coincidence (PEPICO) spectrometer named DELICIOUS II is presented which combines a velocity map imaging apparatus with a Wiley-McLaren time of flight analyzer for the study of gas phase samples in interaction with the synchrotron radiation (SR).
Abstract: We present a photoelectron-photoion coincidence (PEPICO) spectrometer named DELICIOUS II which combines a velocity map imaging apparatus with a Wiley–McLaren time of flight analyzer for the study of gas phase samples in interaction with the synchrotron radiation (SR) This versatile system is capable of providing photoelectron images on mass-selected compounds with kinetic energy resolutions of ΔE/E=5% and a 17 eV bandwidth, as well as threshold photoelectron spectra with a measured resolution of 08 meV, as demonstrated on the 3p−1 ionization of argon This instrument is also employed for threshold PEPICO experiments, allowing the selection of the parent ion’s internal state with sub-meV resolution for light masses (<40 amu) and with typically 2 meV resolution for a mass of 100 amu and with a mass resolving power above 200 The continuous operation of the extraction fields and the independence from the electron’s time of flight are well adapted to the quasicontinuous multibunch mode of the SR This, toge
121 citations
TL;DR: A review of the available theoretical and experimental tools and their performances can be found in this paper, with a particular emphasis on single-photon valence-shell ionization induced by VUV continuous sources such as synchrotron radiation and observed by electron imaging.
104 citations
TL;DR: The last decade has seen photoelectron angular distributions from isolated molecules used for an increasing variety of purposes, including examining details of electron correlation, demonstrating electron diffraction as a structural probe of single molecules, and probing photochemical processes as discussed by the authors.
Abstract: The last decade has seen photoelectron angular distributions from isolated molecules used for an increasing variety of purposes, including examining details of electron correlation, demonstrating electron diffraction as a structural probe of single molecules, and probing photochemical processes. In this article these developments are reviewed and it is shown that the stage is set for another decade of innovation in which we can expect to see exciting results from pump–probe experiments using the emerging XUV and X-ray free-electron laser sources.
100 citations
References
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TL;DR: The Gaussian-2 theoretical procedure (G2 theory) as discussed by the authors was proposed to calculate molecular energies (atomization energies, ionization potentials, and electron affinities) of compounds containing first and second-row atoms.
Abstract: The Gaussian‐2 theoretical procedure (G2 theory), based on a b i n i t i o molecular orbital theory, for calculation of molecular energies (atomization energies, ionization potentials,electron affinities, and proton affinities) of compounds containing first‐ (Li–F) and second‐row atoms (Na–Cl) is presented. This new theoretical procedure adds three features to G1 theory [J. Chem. Phys. 9 0, 5622 (1989)] including a correction for nonadditivity of diffuse‐s p and 2d f basis set extensions, a basis set extension containing a third d function on nonhydrogen and a second p function on hydrogen atoms, and a modification of the higher level correction. G2 theory is a significant improvement over G1 theory because it eliminates a number of deficiencies present in G1 theory. Of particular importance is the improvement in atomization energies of ionic molecules such as LiF and hydrides such as C2H6, NH3, N2H4, H2O2, and CH3SH. The average absolute deviation from experiment of atomization energies of 39 first‐row compounds is reduced from 1.42 to 0.92 kcal/mol. In addition, G2 theory gives improved performance for hypervalent species and electron affinities of second‐row species (the average deviation from experiment of electron affinities of second‐row species is reduced from 1.94 to 1.08 kcal/mol). Finally, G2 atomization energies for another 43 molecules, not previously studied with G1 theory, many of which have uncertain experimental data, are presented and differences with experiment are assessed.
3,216 citations
887 citations
TL;DR: The pBasex algorithm as mentioned in this paper reconstructs the original Newton sphere of expanding charged particles from its two-dimensional projection by fitting a set of basis functions with a known inverse Abel integral, adapted to the polar symmetry of the photoionization process to optimize the energy and angular resolution.
Abstract: We present an inversion method called pBasex aimed at reconstructing the original Newton sphere of expanding charged particles from its two-dimensional projection by fitting a set of basis functions with a known inverse Abel integral. The basis functions have been adapted to the polar symmetry of the photoionization process to optimize the energy and angular resolution while minimizing the CPU time and the response to the cartesian noise that could be given by the detection system. The method presented here only applies to systems with a unique axis of symmetry although it can be adapted to overcome this restriction. It has been tested on both simulated and experimental noisy images and compared to the Fourier-Hankel algorithm and the original Cartesian basis set used by [Dribinski et al.Rev. Sci. Instrum. 73, 2634 (2002)], and appears to give a better performance where odd Legendre polynomials are involved, while in the images where only even terms are present the method has been shown to be faster and simpler without compromising its accuracy.
602 citations
TL;DR: In photoionization of free, unoriented chiral molecules with circularly polarized radiation, a significant circular dichroism has been observed in the photoelectron angular distribution, which leads to an asymmetry in the momentum transfer to the photoions.
Abstract: In photoionization of free, unoriented chiral molecules with circularly polarized radiation, a significant circular dichroism, ie, an asymmetry in the forward-backward electron emission, has been observed in the photoelectron angular distribution This leads also to an asymmetry in the momentum transfer to the photoions The spectra for the left- and right-handed enantiomers of bromocamphor exhibit asymmetries up to several percent which vary as a function of orbital binding energy This enantioselective effect can similarly occur for biomolecules with handedness, like amino acids, and may thus be a contributing factor related to the origin of the terrestrial biomolecular homochirality
305 citations
TL;DR: In this paper, the angular distribution of photoelectrons ejected on absorption of left or right circularly polarized light by a mixture of randomly oriented dextrorotatory and levorotatory optical isomers was analyzed.
Abstract: It is shown that the angular distribution of photoelectrons ejected on absorption of left or right circularly polarized light by a mixture of randomly oriented dextrorotatory and levorotatory optical isomers behaves as $A\ifmmode\pm\else\textpm\fi{}Bcos\ensuremath{\theta}+C{cos}^{2}\ensuremath{\theta}$, where $\ensuremath{\theta}$ is the angle between the photoelectron momentum and photon direction of incidence and $\ifmmode\pm\else\textpm\fi{} Bcos\ensuremath{\theta}$ is introduced by the presence of unequal numbers of each isomer. All coefficients of ${cos}^{n}\ensuremath{\theta}$ are of order $\ensuremath{\alpha}$, and analysis shows that $B$ can be as large as $A$ and $C$.
251 citations