Collision-Energy-Resolved Penning Ionization Electron Spectroscopy of Nitriles:  Conjugation Effects on Interactions with He*(2³S) Metastable Atoms

Abstract

Penning ionization of propionitrile (CH3CH2C⋮N), acrylonitrile (CH2CHC⋮N), and 3-butenenitrile (CH2CHCH2C⋮N) upon collision with He*(23S) metastable atoms has been studied by two-dimensional Penning ionization electron spectroscopy in which Penning electron intensity is measured as a function of both collision energy and electron energy. We have observed a strong negative collision energy dependence of the partial ionization cross sections for ionization from nonbonding and πCN orbitals of all samples studied, which indicates that the interaction potentials between He*(23S) and target molecules are strongly attractive around the cyano group. For π-conjugated acrylonitrile, strong attractive interaction was shown for the πCC orbital region, while the attractive interaction for the πCC orbital region became weak for nonconjugated 3-butenenitrile. The observed results are consistent with calculated model potential curves. The electron density difference for charge transfer was analyzed for the lone pair orbital region where the molecule acts as an electron donor, while the molecule acts as an electron acceptor for the conjugated π orbital region.

Spin−Orbit Coupling Effect and Intramolecular Orbital Interactions: Penning Ionization of CH2BrCl, CHBrCl2, and CH2BrCN by Collision with He*(23S) Metastable Atoms

“…Figure 14. Diagram of the split energy between πCN ⊥ and πCN | bands in UPS, by the intramolecular orbital interactions of σCH,CC, 12,32 σCH,CC(cyclo), 16 nBr, πCC, 12,32 and nS. 14 Second, because the electron density maps for each MO shown in Figures 7-9 are delocalized over several atoms, MOs have mixed character.…”

Penning Ionization of Cyclopropanes by Collision with He*(23S) Metastable Atoms

“…It is known that the n N band shows large enhancement in PIES. 23, 26,46 (2) Although bands 3 and 4 are overlapped in PIES, the component of band 3 is dominant. Thus the slope parameter, m, for band 3 is estimated to be -0.52, and its negative peak shift is ∆E ) -400 meV.…”

Radical-induced fragmentation of phospholipid cations using metastable atom-activated dissociation mass spectrometry (MAD-MS)

“…Penning ionization of precursor lipids in the 1+ charge state is expected to occur at sterically-exposed sites of highest electron density such as lone pairs on oxygen and π-electrons [45, 46]. Therefore, one would expect the new radical and charge to be initially located on carbonyl or phosphate oxygen atoms, as is the case for electron ionization (EI) of neutral lipids [7, 8].…”

“…It is known that in the Penning ionization of gas-phase neutral organics, metastable atoms are attracted to, and therefore ionize at, areas of high electron density [45, 46, 62], which is based on dipole attraction and steric factors at close range [63–66]. The He-MAD spectra presented here indicate that Penning ionization of charged lipids also follows preferential oxidation/activation of the lone pairs on carbonyl or phosphate oxygen atoms and the π-electrons in the unsaturated C=C bonds.…”