Threshold behavior in metastable dissociation of multi-photon ionized thymine and uracil

Microsecond-timescale HNCO loss has been observed from single-color multi-photon ionized pyrimidine nucleobases in the gas phase. Photon energy thresholds for the metastable channels have been measured at 5.55 ± 0.02 eV for thymine and 5.57 ± 0.02 eV for uracil. We argue that these results can be attributed to accessing the molecules’ S1 states with additional vibrational energy matching the threshold energy for HNCO loss from the radical cation. Combined with previous photoionization energies, this enables the S1 adiabatic energies to be deduced: 3.67 ± 0.07 eV for thymine and 3.77 ± 0.07 eV for uracil. These values are consistent with recent calculations

Stabilities of nanohydrated thymine radical cations: insights from multiphoton ionization experiments and ab initio calculations

Multi-photon ionization experiments have been carried out on thymine-water clusters in the gas phase. Metastable H2O loss from T+(H2O)n was observed at n ≥ 3 only. Ab initio quantum-chemical calculations of a large range of optimized T+(H2O)n conformers have been performed up to n = 4, enabling binding energies of water to be derived. These decrease smoothly with n, consistent with the general trend of increasing metastable H2O loss in the experimental data. The lowest-energy conformers of T+(H2O)3 and T+(H2O)4 feature intermolecular bonding via charge-dipole interactions, in contrast with the purely hydrogen-bonded neutrals. We found no evidence for a closed hydration shell at n = 4, also contrasting with studies of neutral clusters

Mapping the complex metastable fragmentation pathways of excited 3-aminophenol+

This work applies the technique of mapping ion detection using a reflectron mass spectrometer against flight-time and reflection voltage to elucidate the complex metastable fragmentation pattern of the biomolecular ion 3-aminophenol+ (3-AP+, C6H7NO+). Multiphoton ionization experiments revealed the excited ion's fragmentation routes for the first time and comparisons with calculated flight-times enabled 18 μs-timescale dissociations to be assigned. These included the rare observation of a double hydrogen loss channel from a fragment ion. Ab initio calculations provided further insights into the most prominent apparent fragmentation sequence: 3-AP+ (m/z 109) → HCO + C5H6N+ (m/z 80) → CNH + C4H5+ (m/z 53) → C2H2 + C2H3+ (m/z 27)

Stability of Multiply-Charged Biomolecular Clusters Formed Upon Interaction with Low-Energy Highly Charged Ions

International audienc

Formation of Anions and Cations Via a Binary-Encounter Process in Oh+ + Ar Collisions : The Role of Dissociative Excitation and Statistical Aspects

International audienc

Electron Capture in O²⁺ + H₂ Collisions at a few keV Impact Energies

International audienc

Electron Capture in O²⁺ + H₂ Collisions at a few keV Impact Energies

International audienc