Soft-x-ray fragmentation studies of molecular ions

Abstract

Abstract. Imaging of photofragments from molecular ions after irradiation by soft X-ray photons has been realized at the ion beam infrastructure TIFF set up at the FLASH facility. Photodissociation of the two-electron system HeH + at 38.7 eV revealed the electronic excitations and the charge-state ratios for the products of this process, reflecting the non-adiabatic dissociation dynamics through multiple avoided crossings among the HeH + Rydberg potential curves. Dissociative ionization of the protonated water molecules H 3 O + and H 5 O + 2 at 90 eV revealed the main fragmentation pathways after the production of valence vacancies in these ionic species, which include a strong three-body channnel with a neutral fragment (OH + H + + H + ) in H 3 O + photolysis and a significant two-body fragmentation channel (photolysis. The measurements yield absolute cross sections and fragment angular distributions. Increased precision and sensitivity of the technique was realized in recent developments, creating a tool for exploring X-ray excited molecular states under highly controlled target conditions challenging detailed theoretical understanding.

Perspectives of Gas Phase Ion Chemistry: Spectroscopy and Modeling

“…The experiments at the FEL facilities aim to study the peculiarities of electronic dynamics, known to be active on attosecond time scales, and the formation/breaking of bonds that occur in the femtosecond regime. Particular attention is paid to the study of the electronic and nuclear motion in photoexcited molecules, the redistribution of the energy stored by the molecule as a result of photo-absorption, and the nuclear dynamics of chemical reactions involving highly excited states in cold molecular ions, in order to mimic the XUV photochemistry of higher planetary atmospheres and interstellar clouds [71].…”

Photoionisation of ions with synchrotron radiation: from ions in space to atoms in cages

“…A more general approach is to store the ions for a sufficiently long time before exposing them to the ionizing photon beam. In a few experimental arrangements, ion traps are used for this purpose [29,44]. A draw-back of the trapping technique is that the statistical quality of the results suffers severely from the massive particle losses from the trap during the ion-storage time.…”

Coincidence spectroscopy: Past, present and perspectives

“…In view of the requirement of a low event rate and the benefits of a high event rate of the ionization source, careful scrutiny with respect to the feasibility of any coincidence experiment is advised. One field were it has potential merits is the investigation of very thin targets, such as ion beams [212] or electrospray sources [213]. Moreover, if e.g.…”