Soft X-ray Induced Production of Neutral Fragments in High-Rydberg States at the O 1s Ionization Threshold of the Water Molecule

Abstract

Dissociation of water molecules after soft X-ray absorption can yield neutral fragments in high-Rydberg (HR) states. We have studied the production of such fragments by field ionization and ion time-of-flight (TOF) spectrometry. Neutral HR fragments are created at all resonances below the O 1s ionization potential (IP) and particularly within 1 eV above the O 1s IP. The latter effect is due to the recapture of the O 1s photoelectrons into HR orbitals of the molecular water ion after the emission of a fast Auger electron. H 2 O + (HR) fragments subsequently dissociate, yielding neutral H(HR) and O(HR) fragments, as were found by measuring the TOF spectra by pulsed field ionization. Such measurements were carried out at the O 1s → 4a 1 and 2b 2 resonances as well as just above the O 1s IP. The TOF spectra also reveal two series of oscillatory structures that are attributed to quantum beats involving Lyman emission in one of the series and field ionization of H(HR) fragments in the other series.

Core–shell excitation of isoxazole at the C, N, and O K-edges – an experimental NEXAFS and theoretical TD-DFT study

“…22,46 Since the appearance of the above-threshold maxima is connected to the corresponding IPs (only very slow 1s photoelectrons are efficiently recaptured), one can use their positions to estimate unknown core binding energies. For that purpose, we compared the well-known CEBEs with the fitted maxima of the above-threshold peaks observed in the studies of methane, 22 carbon dioxide, 23 dinitrogen, 46 and water 47 molecules. We calculated that the IPs, on average, lie (230 AE 150) meV below the above-threshold maxima.…”

Two-body dissociation of isoxazole following double photoionization – an experimental PEPIPICO and theoretical DFT and MP2 study

“…38 It consists of a modified Wiley–McLaren TOF spectrometer used initially to detect photoelectron–photoion coincidences and neutral-particle-photoion coincidences. 39 We have also exploited this apparatus to measure the yields and TOF spectra of neutral high-Rydberg fragments at the K edges of the CO 2 , 40 H 2 O, 41 and isoxazole 34 molecules. In a rearranged configuration, this device can also record PEPIPICO spectra.…”

Neutral Dissociation of Pyridine Evoked by Irradiation of Ionized Atomic and Molecular Hydrogen Beams

“…The interaction of ions with biological molecules in the gas phase leads to ionization, excitation, charge transfer, complex formation, and dissociation processes that produce neutral and ionic products [ 18 , 19 , 20 , 21 , 22 , 23 , 24 , 25 , 26 , 27 , 28 , 29 , 30 , 31 , 32 ]. The mass spectrometric methods are developed to probe the charged entities [ 22 , 39 ], as well as to study neutral fragments in high-Rydberg states but without identifying their final states [ 40 , 41 ]. Conversely, excited products can be identified by detecting their emission [ 42 , 43 ].…”