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

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 is ionization potential (IP) and particularly within 1 eV above the O is IP. The latter effect is due to the recapture of the O is photoelectrons into HR orbitals of the molecular water ion after the emission of a fast Auger electron. H2O+(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 is 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.

Automated summary

The dissociation of water molecules after soft X-ray absorption can generate neutral fragments in high-Rydberg states, with a special emphasis on the region within 1 eV above the O ionization potential. The process involves complex reactions, including the recapture of photoelectrons and the emission of fast Auger electrons.