Vibrational state dependence of β and D asymmetry parameters: The case of the highest occupied molecular orbital photoelectron spectrum of methyl-oxirane

Enantioselective fragmentation of an achiral molecule in a strong laser field

Chirality is omnipresent in living nature. On the single molecule level, the response of a chiral species to a chiral probe depends on their respective handedness. A prominent example is the difference in the interaction of a chiral molecule with left or right circularly polarized light. In the present study, we show by Coulomb explosion imaging that circularly polarized light can also induce a chiral fragmentation of a planar and thus achiral molecule. The observed enantiomer strongly depends on the orientation of the molecule with respect to the light propagation direction and the helicity of the ionizing light. This finding might trigger new approaches to improve laser-driven enantioselective chemical synthesis.

Intense Vibronic Modulation of the Chiral Photoelectron Angular Distribution Generated by Photoionization of Limonene Enantiomers with Circularly Polarized Synchrotron Radiation

Photoionization of the chiral monoterpene limonene has been investigated using polarized synchrotron radiation between the adiabatic ionization threshold, 8.505 and 23.5 eV. A rich vibrational structure is seen in the threshold photoelectron spectrum and is interpreted using a variety of computational methods. The corresponding photoelectron circular dichroism-measured in the photoelectron angular distribution as a forward-backward asymmetry with respect to the photon direction-was found to be strongly dependent on the vibronic structure appearing in the photoelectron spectra, with the observed asymmetry even switching direction in between the major vibrational peaks. This effect can be ultimately attributed to the sensitivity of this dichroism to small phase shifts between adjacent partial waves of the outgoing photoelectron. These observations have implications for potential applications of this chiroptical technique, where the enantioselective analysis of monoterpene components is of particular interest.

Conformational effects in photoelectron circular dichroism

Photoelectron circular dichroism (PECD) is a novel type of spectroscopy, which presents surprising sensitivity to conformational effects in chiral systems. While classical photoelectron spectroscopy mainly responds to conformational effects in terms of energy level shifts, PECD provides a rich and detailed response to tiny changes in electronic and structural properties by means of the intensity dispersion of the circular dichroism as a function of photoelectron kinetic energy. In this work, the basics of PECD will be outlined, emphasizing the role of interference from the [Formula: see text] outgoing partial wave of the photoelectron in the PECD transition matrix element, which is responsible for the extreme sensitivity to conformational effects. Examples using molecular systems and interfaces will shed light on the powerful application of PECD to classical conformational effects such as group substitution, isomerism, conformer population and clustering. Moreover, the PECD results will be reported in challenging new fields where conformations play a key role, such as vibrational effects, transient chirality and time- resolved experiments. To date, PECD has mostly been based on synchrotron radiation facilities, but it also has a future as a table-top lab experiment by means of multiphoton ionization. An important application of PECD as an analytical tool will be reported. The aim of this review is to illustrate that in PECD, the presence of conformational effects is essential for understanding a wide range of effects from a new perspective, making it different from classical spectroscopy.

FTIR spectra and density functional theory P.E.D. assignments of oxiranes in Ar matrix at 12 K

The FTIR spectra of a series of oxiranes were studied in Ar matrix at 12K. The interpretation of the spectra was accomplished on the basis of density functional theory calculations employing the 6-311++G(3df,3pd) basis set with the B3LYP functional. Potential energy distribution was carried out for each molecule employing the B3LYP/6-311++G(3df,3pd) force field and a non-redundant definition of internal coordinates. The study of the FTIR spectra led to the reassignment of some vibrational modes of the molecules. The FTIR spectrum of trifluoroepoxypropane measured in Ar matrix and its assignment is reported for the first time.

Franck–Condon factors—Computational approaches and recent developments

Algorithms and methodologies for the calculation of Franck–Condon integrals are reviewed. Starting from the standard approach based on the Cartesian representation of the normal modes and the use of Duschinsky's transformation and recursion formulas, methods for treating large displacements of the equilibrium positions and anharmonic and non-Condon effects are considered. Finally, focusing attention on problems arising from the use of recurrence relations, some of the proposed solutions are critically reviewed along with new alternative approaches.

Vibrationally induced inversion of photoelectron forward-backward asymmetry in chiral molecule photoionization by circularly polarized light

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-β) 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.

Resonant circular dichroism of chiral metal-organic complex

A sizable enhancement of the circular dichroism in photoelectron spectroscopy has been measured and computed for the metal complex Δ-cobalt(III) tris-acetylacetonate highest occupied molecular orbital state in the region of the Co 3p→3d Fano resonance. In the resonance the dichroism reaches the maximum value of 5% and even changes its sign as compared to the direct photoionization channel. We ascribe this enhancement to electron correlation processes, namely, with the coupling between discrete excitations and the continuum, which is correctly described in the time dependent density functional theory (TDDFT) framework. These findings open new physical aspects of photoelectron circular dichroism that now can be interpreted not only via the simple direct ionization, but also through more complex electron correlation processes.

Circular Dichroism in Ion Yields in Multiphoton Ionization of (R)-Propylene Oxide Employing Femtosecond Laser Pulses

The feasibility of measuring circular dichroism (CD) in ion yields is demonstrated in multiphoton ionization employing femtosecond laser radiation for the first time. CD values for (R)-propylene oxide are reported at 738 nm, 810 nm and 878 nm. The data suggest the possibility of resonance contributions at 810 nm. At the other wavelengths the CD appears to originate from non-resonant multiphoton ionization. Possible implications of measuring non-resonant CD are discussed.