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

Fanood, Mohammad M. Rafiee; Ganjitabar, Hassan; Garcia, Gustavo A.; Nahon, Laurent; Turchini, S.; Powis, Ivan

doi:10.1002/cphc.201701248

Cited by 17 publications

(17 citation statements)

References 61 publications

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“…The spectroscopic assignment of the structures observed on these fingerprints is beyond the scope of this paper. Let us simply mention that the sign changes in the low-energy range PEELD can result from vibrational excitation of the ion, as observed in PECD 29 , 35 , 36 , but also from low-energy electron scattering. However, one-dimensional (1D) fingerprints are indeed enough to measure the composition of a multi-component mixture, offering the opportunity to perform faster analysis for real-time monitoring.…”

Section: Resultsmentioning

confidence: 99%

Real-time determination of enantiomeric and isomeric content using photoelectron elliptical dichroism

et al. 2018

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The fast and accurate analysis of chiral chemical mixtures is crucial for many applications but remains challenging. Here we use elliptically-polarized femtosecond laser pulses at high repetition rates to photoionize chiral molecules. The 3D photoelectron angular distribution produced provides molecular fingerprints, showing a strong forward-backward asymmetry which depends sensitively on the molecular structure and degree of ellipticity. Continuously scanning the laser ellipticity and analyzing the evolution of the rich, multi-dimensional molecular signatures allows us to observe real-time changes in the chemical and chiral content present with unprecedented speed and accuracy. We measure the enantiomeric excess of a compound with an accuracy of 0.4% in 10 min acquisition time, and follow the evolution of a mixture with an accuracy of 5% with a temporal resolution of 3 s. This method is even able to distinguish isomers, which cannot be easily distinguished by mass-spectrometry.

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Section: Resultsmentioning

confidence: 99%

Real-time determination of enantiomeric and isomeric content using photoelectron elliptical dichroism

et al. 2018

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“…The highest occupied molecular orbital (HOMO) is the carbon double bond (C=C) in the cyclohexene ring. is the ground state cation of limonene with an ionization energy of 8.54 eV 37 , 38 . The first excited cationic state is a molecular orbital having an ionization energy of and belongs to C=C double bond of isopropenyl group.…”

Section: Resultsmentioning

confidence: 99%

“…In absorption CD, it is attributed to the Cotton effect 49 , 50 , a change in the extinction coefficients of S- and R-limonene for right and left circularly polarized light 5 , 49 . In single and multi-photon PECD of limonene, varying the photon energy led to (a) modulation of the chiral signal mirroring the principal vibrational features observed in the photoelectron spectrum, and (b) flipping of the forward–backwards asymmetry in the angular emission of electrons relative to the photon beam direction 30 , 37 , 38 . The wavelength effects of the chiral signal are attributed to the excitation of vibronic states of the cation and/or intermediate electronic states of the neutral molecule.…”

Section: Discussionmentioning

confidence: 97%

“…The elliptically polarized laser field induces electric and magnetic transitions (orange arrows) in these highly excited states that subsequently undergo field ionization. The energy levels were obtained from limonene photoelectron spectrum 37 , 38 . ( c ) Schematic showing the electron trajectory in an elliptically polarized field along with asymmetric transverse momentum spread.…”

Section: Discussionmentioning

confidence: 99%

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Chiral discrimination by recollision enhanced femtosecond laser mass spectrometry

Bégin

Alsaawy

Bhardwaj

2020

Sci Rep

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chiral molecules and their interactions are critical in a variety of chemical and biological processes. circular dichroism (cD) is the most widely used optical technique to study chirality, often performed in a solution phase. However, CD has low-efficiency on the order of 0.01-1%. therefore, there is a growing need to develop high-efficiency chiroptical techniques, especially in gas-phase, to gain background-free in-depth insight into chiral interactions. By using mass spectrometry and strongfield ionization of limonene with elliptically polarized light, we demonstrate an efficient chiral discrimination method that produces a chiral signal of one to two orders of magnitude higher than the conventional cD. the chiral response exhibits a strong dependence on wavelength in the range of 1,300-2,400 nm, where the relative abundance of the ion yields alternates between the two enantiomers. The origin of enhanced enantio-sensitivity in intense laser fields is attributed to two mechanisms that rely on the recollision dynamics in a chiral system: (1) the excited ionic state dynamics mediated either by the laser field or by the recollision process, and (2) non-dipole effects that alter the electron's trajectories. our results can serve as a benchmark for testing and developing theoretical tools involving non-dipole effects in strong-field ionization of molecules. Chiral molecules lack S n symmetry (improper rotation axis) due to the presence of a chiral center in which an atom is connected to four different groups of atoms 1. Consequently, there is a handedness to the molecule. The left-and right-handed molecules are non-superimposable mirror images of each other, called enantiomers. They have identical physical and chemical properties making it difficult to differentiate them. Chiral discrimination requires an interaction between two chiral systems-a chiral reagent with known handedness that can induce enantio-selectivity in the second chiral system. In nature, bio-molecules such as amino acids that make up life on earth are homochiral, where one enantiomer exists predominantly over the other due to asymmetric interactions 2. Homochirality plays a pivotal role in our daily life by serving as a chiral reagent for enantio-selectivity. For example, olfactory receptors in our nose, responsible for the sense of smell, interact differently with the two enantiomers of a chiral system. For instance, the right-handed enantiomer of limonene has an orange odour while the left-handed enantiomer has a lemon odour 3. In practice, enantio-selectivity can be achieved using circularly polarized light (CPL) as a chiral reagent. CD is one of the most widely used chiroptical techniques. It arises due to the coupling of the electric and magnetic dipole transitions, thereby resulting in a differential absorption of left-and right-circularly polarized light 1,4-8. CD has low-efficiency on the order of 0.01-1% because magnetic dipole transitions are involved 9-12. Moreover, CD measurements are mostly conducted in solution phase, making it diffi...

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“…In our experimental conditions we expect the first two conformers of limonene to be present 31 . These conformers only differ by a few kJ/mol and are not distinguished in PES and PECD measurements in one-photon ionization close to the threshold (< 10 eV) 6 .…”

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confidence: 88%

Multiphoton photoelectron circular dichroism of limonene with independent polarization state control of the bound-bound and bound-continuum transitions

Beaulieu

Comby

Descamps

et al. 2018

The Journal of Chemical Physics

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Photoionization of randomly oriented chiral molecules with circularly polarized light leads to a strong forward/backward asymmetry in the photoelectron angular distribution. This chiroptical effect, referred to as Photoelectron Circular Dichroism (PECD), was shown to take place in all ionization regimes, from single photon to tunnel ionization. In the Resonance Enhanced Multiphoton Ionisation (REMPI) regime, where most of the table-top PECD experiments have been performed, understanding the role of the intermediate resonances is currently the subject of experimental and theoretical investigations. In an attempt to decouple the role of bound-bound and bound-continuum transitions in REMPI-PECD, we photoionized the (+)-limonene enantiomer using two-color laser fields in [1+1'] and [2+2'] ionization schemes, where the polarization state of each color can be controlled independently. We demonstrate that the main effect of the bound-bound transition is to break the sample isotropy by orientation-dependent photoexcitation, in agreement with recent theoretical predictions. We show that the angular distribution of PECD strongly depends on the anisotropy of photoexcitation to the intermediate state, which is different for circularly and linearly polarized laser pulses. On the contrary, the helicity of the pulse that drives the bound-bound transition is shown to have a negligible effect on the PECD. 1 arXiv:1801.08394v2 [physics.chem-ph] 31 Aug 2018Photoelectron circular dichroism (PECD) is a chiroptical effect which was theoretically predicted in the 1970's 1 . Unlike most chiroptical phenomena, which rely on magnetic dipole or electric quadrupole effects, PECD can be fully described within the framework of the electric dipole approximation. As a consequence, PECD is several orders of magnitude larger than conventional chiroptical effects, which are in general extremely weak and thus difficult to use for studies in gas-phase samples. The first experimental observation of PECD from an ensemble of randomly oriented chiral molecules was performed in 2001, using Vacuum Ultra Violet (VUV) synchrotron radiation 2 . Since then, many studies relying on single photon ionization have been conducted, showing that PECD is a powerful probe of molecular chirality (for a review see 3 ), sensitive to electronic structure 4 , vibrational excitation 5,6 , molecular conformation 7-9 , structural isomerism 10,11 , clustering 12 as well as chemical substitution 13,14 .Lately, it was also demonstrated that single photon PECD experiments could be performed using table-top femtosecond elliptically polarized VUV sources from resonant high-order harmonic generation 15 . Recently, a whole new field of PECD studies emerged, relying on the use of UV, visible or IR table-top femtosecond laser sources. In two pioneering experiments, circularly polarized femtosecond UV pulses were used to photoionize enantiopure chiral molecules in a [2+1]Resonant Enhanced Multiphoton Ionisation (REMPI) scheme, and led to the observation of large PECDs, in the 10% range ...

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

Cited by 17 publications

References 61 publications

Real-time determination of enantiomeric and isomeric content using photoelectron elliptical dichroism

Real-time determination of enantiomeric and isomeric content using photoelectron elliptical dichroism

Chiral discrimination by recollision enhanced femtosecond laser mass spectrometry

Multiphoton photoelectron circular dichroism of limonene with independent polarization state control of the bound-bound and bound-continuum transitions

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