Fluorescence emission following core excitations in the water molecule

Abstract

Photon-induced fluorescence spectroscopy has been used to study the fragmentation of the water molecule at the O 1s edge. Fluorescence emission has been observed from the neutral fragments H, O and OH as well as from the ionic fragments O+ and OH+. The extracted fluorescence yields of the H Lyman-α emission and O 2p3(4S)3p(3P) → 2p3(4S)3s(3S) transitions show the same structures as the total ion yield spectrum but with different relative intensities. The most intense fluorescence emission is restricted to the region of the core excitations, while above the O 1s ionization limit the signal is much weaker (in the case of H) or below the detection limit (O, OH and OH+). The fluorescence emission is concluded to follow from the following general cascade: the core-excited states decay by resonant Auger transitions, the final states reached undergo dissociation into ionic and neutral fragments, and fluorescence occurs from excited fragments. In the case of the OH (A2Σ+ → X2Π) emission, the decay of core-excited states through soft x-ray emission may also be responsible for the observed fluorescence.

Production of excited H atoms at the C 1sedge of the methane molecule studied by VUV-photon–photoion and metastable-fragment–photoion coincidence experiments

“…Emission has also been found to persist while crossing the core IP, after which it diminishes gradually as a function of photon energy. That behavior has been attributed to recapture processes following core ionization and Auger decay [10,11]. All in all, low-energy fluorescence emission after core excitation and ionization in small molecules can be explained using the same mechanisms as the production of metastable fragments.…”

Photolysis of water-radical ions H2O+in the xuv: Fragmentation through dicationic states

“…The water dication (H 2 O 2+ ) has previously been experimentally investigated exclusively in studies of double ionization of neutral H 2 O with projectiles of ions [19][20][21][22][23][24], electrons [25][26][27][28], and photons [29][30][31][32][33][34][35][36][37][38][39]. Theoretically, the water dications have been the subject of several studies [40][41][42][43][44].…”

UV-visible emission as a probe of core excitations applied to the furan and carbon dioxide molecules

“…It was shown for the core-excited water molecule that Lyman emission can follow when the core hole decays via spectator resonant Auger transitions [14]; the same conclusion is also valid for Balmer emission. If the core hole decayed through radiative channels, the final states would not have enough internal energy so that a bond could be broken and an excited H fragment released.…”