A velocity map imaging spectrometer for measuring absolute differential cross sections for ion-induced electron emission from molecules.

In this paper, we present a newly developed crossed beam experimental setup that utilizes the velocity map imaging (VMI) technique to simultaneously measure both the kinetic energy and emission angle of electrons emitted from atoms or molecules upon ion collision. The projectile ion beam with keV to MeV kinetic energy orthogonally crosses the neutral target beam produced by an effusion cell. The emitted electrons are extracted and analyzed by a multi-electrode VMI spectrometer.

Thermal desorption effects on fragment ion production from multi-photon ionized uridine and selected analogues.

Experiments on neutral gas-phase nucleosides are often complicated by thermal lability. Previous mass spectrometry studies of nucleosides have identified enhanced relative production of nucleobase ions ( uracil from uridine) as a function of desorption temperature to be the critical indicator of thermal decomposition. On this basis, the present multi-photon ionization (MPI) experiments demonstrate that laser-based thermal desorption is effective for producing uridine, 5-methyluridine, and 2'-deoxyuridine targets without thermal decomposition.

Multiple valence electron detachment following Auger decay of inner-shell vacancies in gas-phase DNA.

We have studied soft X-ray photoabsorption in the doubly deprotonated gas-phase oligonucleotide [dTGGGGT-2H]. The dominating decay mechanism of the X-ray induced inner shell vacancy was found to be Auger decay with detachment of at least three electrons, leading to charge reversal of the anionic precursor and the formation of positively charged photofragment ions. The same process is observed in heavy ion (12 MeV C) collisions with [dTGGGGT-2H] where inner shell vacancies are generated as well, but with smaller probability.

Formation of resonances and anionic fragments upon electron attachment to benzaldehyde.

Benzaldehyde is a simple aromatic aldehyde and has a wide range of applications in the food, pharmaceutical, and chemical industries. The positive electron affinity of this compound suggests that low-energy electrons can be easily trapped by neutral benzaldehyde. In the present study, we investigated the formation of negative ions following electron attachment to benzaldehyde in the gas-phase.

Dipole-Supported Electronic Resonances Mediate Electron-Induced Amide Bond Cleavage.

Dissociative electron attachment (DEA) plays a key role in radiation damage of biomolecules under high-energy radiation conditions. The initial step in DEA is often rationalized in terms of resonant electron capture into one of the metastable valence states of a molecule followed by its fragmentation. Our combined theoretical and experimental investigations indicate that the manifold of states responsible for electron capture in the DEA process can be dominated by core-excited (shake-up) dipole-supported resonances.