Photoionization and dissociation of the monoterpene limonene: mass spectrometric and computational investigation

Abstract

The photoionization of the monoterpene limonene has been studied using tunable vacuum ultraviolet synchrotron radiation in the region from the threshold for ionization of the parent molecule up to 15.5 eV. The adiabatic ionization energy of limonene is derived from photoionization efficiency spectrum and found to be 8.27 eV, compared with the density functional theory calculations which yields a value of 8.08 eV (B3LYP/6-311++G). Primary dissociation pathways of the parent molecule ions are investigated by experimental observations and theoretical calculations. Most of the fragmentation channels occur via a rearrangement reaction prior to dissociation. Transition structures and intermediates for those isomerization processes are also determined.

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

“…As seen in Figure , at 10.0 eV there are very weak (≪1 %) peaks at 93/95 amu and 121 amu. The complete lack of fragmentation for h ν≤9.5 eV contrasts with our own earlier photoionization studies of limonene and the more recent molecular beam work of Fang et al . which both show more significant amounts of “94” amu, 121 amu, and other fragment masses, all with apparent onsets in the 9–9.3 eV region.…”

“…Using B3LYP/6–311++G calculations Fang et al . are able to suggest relatively low thermodynamic thresholds for m / z 94 and m / z 121 dissociation channels, but with transition states that create significant kinetic barriers.…”

“…The remaining orbitals are more σ‐bonding in character, and may be expected to lie deeper, but the photoelectron spectroscopy has not, to our knowledge been extended beyond the composite X‐band. The vacuum ultraviolet (VUV) dissociative ionization has, however, been reported running to somewhat higher ionization energies …”

“…The vacuum ultraviolet (VUV) dissociative ionization has, however,b een reported running to somewhat higher ionization energies. [16,18] The VUV absorption spectrum of limonene [15,17] commences at l % 220 nm with af irst Rydberg transition assigned as 2p! 3s.…”

Mass spectrometric approaches for chemical characterisation of atmospheric aerosols: critical review of the most recent advances

“…Fang et al used VUV photoionisation in a single-particle aerosol time-of-flight mass spectrometer (ATOFMS) for characterisation of the composition of SOAs produced through photooxidation of toluene in a smog chamber. [48,49] Robinson et al [50] reported coupling of a softer ionisation source with an Aerodyne aerosol mass spectrometer (AMS). In that study, a metastable atom bombardment (MAB) ionisation source was incorporated so the system could be readily switched between MAB and traditionally used electron ionisation (EI).…”