We studied the photoionization of 2-pyridone and its tautomer, 2-hydroxypyridine by means of VUV synchrotron radiation coupled to a velocity map imaging electron/ion coincidence spectrometer. The photoionization efficiency (PIE) spectrum is composed of steps. The state energies of the [2-pyridone]⁺ cation in the ground and à excited electronic states, as well as of the [2-hydroxypyridine]⁺ cation in the electronic ground state, are determined. The slow photoelectron spectra (SPES) are dominated by the 0⁰ ₀ transitions to the corresponding electronic states together with several weaker bands corresponding to the population of the pure or combination vibrational bands of the cations. These vibrationally-resolved spectra compare very well with state-of-the-art calculations. Close to the ionization thresholds, the photoionization of these molecules is found to be mainly dominated by a direct process whereas the indirect route (autoionization) may contribute at higher energies.

We report highly selective covalent bond modifications in collisions between keV alpha particles and van der Waals clusters of ${\mathrm{C}}_{60}$ fullerenes. Surprisingly, $\mathrm{C}_{119}{}^{+}$ and $\mathrm{C}_{118}{}^{+}$ are the dominant molecular fusion products. We use molecular dynamics simulations to show that $\mathrm{C}_{59}{}^{+}$ and $\mathrm{C}_{58}{}^{+}$ ions—effectively produced in prompt knockout processes with ${\mathrm{He}}^{2+}$—react rapidly with ${\mathrm{C}}_{60}$ to form dumbbell $\mathrm{C}_{119}{}^{+}$ and $\mathrm{C}_{118}{}^{+}$. Ion impact on molecular clusters in general is expected to lead to efficient secondary reactions of interest for astrophysics. These reactions are different from those induced by photons.

DNA oligonucleotide ions forming G-quadruplex structures were studied in the gas phase using IRMPD spectroscopy. Data interpretation on these large biomolecule ions was made using carefully chosen control experiments. The major finding is a fingerprint of hydrogen bonding in the gas phase in the guanine C6=O6 stretching mode, that allows probing the conservation of G-quartets in the gas phase. The experiments demonstrate the conservation of G-quadruplex hydrogen bonds in the human telomeric sequence d(TTAGGG)4. ; Peer reviewe

Electron capture by both bare and microsolvated small peptide dications was investigated by colliding these ions with sodium vapor in an accelerator mass spectrometer to provide insight into processes that occur on the microsecond time frame. Survival of the intact peptide monocation after electron capture depends strongly on molecular size. For dipeptides, no intact reduced species were observed; the predominant ions correspond to loss of hydrogen and ammonia. In contrast, the intact reduced species was observed for larger peptides. Calculated structures indicate that the diprotonated dipeptide ions form largely extended structures with low probability of internal ionic hydrogen bonding (i.e., charge solvation) whereas internal ionic H-bonding occurs extensively for larger peptide dications. Solvation of the peptide ions with between one to seven methanol molecules reduces the total extent of H loss even for dipeptides where intact reduced species can survive more than a microsecond after electron capture. The yield of ions corresponding to cleavage of N-C_α bonds (c ⁺ and z ^+· ions) does not depend strongly on peptide size but decreases with the extent of microsolvation for the dipeptide dications. H-bonding appears to play an important role for the survival of the intact reduced ions but less so for the formation of c ⁺ and z ^+· ions. Our results indicate that electron capture predominantly occurs at the ammonium groups (at least 70 to 80%), and provides important new insights into the electron capture dissociation process.