Enantioselective femtosecond laser photoionization spectrometry of limonene using photoelectron circular dichroism

Abstract

Limonene is ionized by circularly polarized 420 nm femtosecond laser pulses. Ion mass and photoelectron energy spectra identify the dominant (2 + 1) multiphoton ionization mechanism, aided by TDDFT calculations of the Rydberg excitations. Photoelectron circular dichroism measurements on pure enantiomers reveal a chiral asymmetry of ±4 %.

Universality of photoelectron circular dichroism in the photoionization of chiral molecules

“…This indicates a clear modification of the ionization scheme. Indeed, changing λ from 409 to 396 nm brings different Rydberg states of limonene into resonance with w 2 absorption from the HOMO: from 3s to the lowest 3p state according to the assignment made in [18], or from the lowest 3p to the intermediate 3p state according to [11]. Comparison of figures 1(d) and (f) unambiguously shows that similar PECDs are obtained at both wavelengths for the HOMO, with the same sign and in the 4% range.…”

“…Comparison of figures 1(d) and (f) unambiguously shows that similar PECDs are obtained at both wavelengths for the HOMO, with the same sign and in the 4% range. Furthermore, (2+1)-REMPI at 420nm, involving vibrationally excited 3s state as the intermediate step, also led to~4% PECD [11]. All of this proves that PECD is not sensitive to either the electronic character or the strength of the intermediate resonance involved in UV-MPI of limonene.…”

“…Lux et al [9] measured a ∼15% PECD in (2+1) resonance-enhanced multiphoton ionization (REMPI) of fenchone and camphor where two photon absorption brings the molecule into an electronic excited state while the third photon ionizes the system. Since this pioneering experiment, REMPI-PECD has been measured in other compounds, in (2+1) [10][11][12] and (3+1) [13] configurations. Recently, Lux et al observed PECD in the first above threshold ionization (ATI) peak in a (2+2) scheme [14].…”

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

“…have measured the gas phase absorption circular dichroism (CD) of limonene in this region and Logé and Boesl have correspondingly measured the CD (in the ion yield) generated by 2 photon laser ionization of R‐limonene enantiomer at 213 nm. Two photon resonant (2+1) laser multiphoton ionization, for λ ≈400 nm, has also been used to investigate the PECD of limonene enantiomers by examining the forward‐backward asymmetry in the photoelectron angular distribution that results . Although nominally exciting through the same intermediate states at the two photon level, the PECD asymmetry is several orders of magnitude greater than the absorption CD owing to the former effect arising in the pure electric dipole approximation .…”

“…Twop hotonr esonant (2 + 1) laser multiphoton ionization,f or l % 400 nm, has also been used to investigate the PECD of limonene enantiomersb ye xaminingt he forward-backward asymmetry in the photoelectron angular distribution that results. [20][21][22] Although nominally exciting through the same intermediate states at the two photon level, the PECD asymmetryi ss everal orders of magnitude greater than the absorption CD owing to the former effecta rising in the pure electric dipole approximation. [23] Such an enhanced asymmetry for VUV PECD, in the 1%-40 %r ange, is by now well established.…”