Photoelectron Circular Dichroism of Bicyclic Ketones from Multiphoton Ionization with Femtosecond Laser Pulses

Abstract

Photoelectron circular dichroism (PECD) is a CD effect up to the ten-percent regime and shows contributions from higher-order Legendre polynomials when multiphoton ionization is compared to single-photon ionization. We give a full account of our experimental methodology for measuring the multiphoton PECD and derive quantitative measures that we apply on camphor, fenchone and norcamphor. Different modulations and amplitudes of the contributing Legendre polynomials are observed despite the similarity in chemical structure. In addition, we study PECD for elliptically polarized light employing tomographic reconstruction methods. Intensity studies reveal dissociative ionization as the origin of the observed PECD effect, whereas ionization of the intermediate resonance is dominating the signal. As a perspective, we suggest to make use of our tomographic data as an experimental basis for a complete photoionization experiment and give a prospect of PECD as an analytic tool.

Wavelength dependent photoelectron circular dichroism of limonene studied by femtosecond multiphoton laser ionization and electron-ion coincidence imaging

“…2) has shown that for all but the 392 nm 1 eV kinetic energy result the chiral b3 and b5 coefficients are effectively zero, to within close to the statistical uncertainty. This contrasts with studies of camphor, where the magnitude of b3 is comparable to that of b1 8,11 although it parallels observations on MP-PECD of methyl oxirane. 9 Intuitively, b3  0 might appear to suggest no multiphoton character, or at least that the 2-photon intermediate was not aligned, so contributed no additional anisotropy.…”

“…[1][2][3] Initially developed using synchrotron radiation [4][5][6] , more recently the PECD technique has expanded its reach significantly by utilizing tabletop ultrafast laser-based radiation. [7][8][9][10][11][12][13] It has been shown in the various chiral molecules studied by PECD that a pronounced forward-backward asymmetry in the photoelectron angular distribution can be observed, typically ranging from 1-40% of the total photoionization yield. This PECD asymmetry is two to three orders of magnitude larger than the typical asymmetry observed in (vibrational/electronic) circular dichroism.…”

Determination of accurate electron chiral asymmetries in fenchone and camphor in the VUV range: sensitivity to isomerism and enantiomeric purity

“…Pre--alerted by previous reports 25,37 that similarly sourced commercial fenchone samples may not be enantiopure, and by our own experience with camphor (above), we took additional steps to verify purity of our fenchone samples. The two different enantiomeric samples of fenchone were analyzed by GC×GC--TOFMS to obtain a precise value of the e.e.…”

Mass‐Selected Circular Dichroism of Supersonic‐Beam‐Cooled [D4]‐(R)‐(+)‐3‐Methylcyclopentanone

“…CD utilizes the absorption difference of left‐ and right‐circularly polarized light depending on the enantiomer of a chiral molecule (CD effect). It also allows several combinations with other nonenantioselective analysis techniques, such as angular‐resolved photoelectron spectroscopy, nonlinear two‐photon spectroscopy, and mass spectrometry (MS) …”