Effect of fluoro substitution on the fragmentation of the K‐shell excited/ionized pyridine studied by electron impact

Abstract

Fragmentation of the pyridine ring followed by K-shell excitation/ionization has been studied with 2-fluoropyridine (2FPy) by electron impact. Ab initio molecular orbital (MO) calculations were also carried out to investigate the electronic states correlating with specific fragment ions. The fragment ions are produced characteristically at the N 1s edge, while the spectra observed at the F 1s and C 1s edges exhibit a small difference from that at the valence ionization. The production of the C(4)H(2)(+), C(4)H(3)(+) and C(4)H(2)F(+) ions indicates that the cleavage of the N-C6 and C2-C3 bonds or the N-C2 and C5-C6 bonds is likely to occur after the N 1s excitation/ionization. Ab initio MO calculations indicate that the former fission is likely to proceed through the n(N)(1)π(2)(1)π(3)(2) and n(N)(0)π(2)(2)π(3)(2) excited states of the parent molecular dication. On the other hand, the breakage of the N-C2 and C4-C5 bonds, which specifically proceeds at the N 1s edge for 2-methylpyridine, does not occur for 2FPy. The present calculation reveals that the products of this channel are unstable by the electronegativity of fluorine and that the relative energy of the Auger-final states of 2FPy is lowered by the reorganization and electron correlation effects.

Near-Edge X-ray Absorption Fine Structure Spectra and Site-Selective Dissociation of Phenol

“…Site-specific fragmentation of aromatic molecules has been found for 2-amino-3-methylpyridine, 2-fluoropyridine, and pyrimidine derivatives − following excitation of electrons from C 1s and N 1s orbitals. The dissociation of phenol is of great interest − because phenol is the chromophore of amino acid tyrosine.…”

“…When a core electron of oxygen is excited to σ*(O−CH 3 ), cleavage of the O−CH 3 bond is enhanced, but the C−OCH 3 bond is more likely to break when the core electron is excited to σ*(C−OCH 3 ). 21 Site-specific fragmentation of aromatic molecules has been found for 2-amino-3-methylpyridine, 33 2-fluoropyridine, 34 and pyrimidine derivatives 35−38 following excitation of electrons from C 1s and N 1s orbitals. The dissociation of phenol is of great interest 39−43 because phenol is the chromophore of amino acid tyrosine.…”