Bond rearrangement during Coulomb explosion of water molecules

Abstract

Bond rearrangement, namely the dissociation of water ions into H + 2 + O (q−1)+ (q=1-4) following fast ion-impact ionization, unexpectedly occurs following multiple ionization of water in spite of the presumably fast "Coulomb explosion" of the transient molecular ion. Furthermore, the branching ratio of bond rearrangement is found to be nearly equal for each level of ionization, q. In addition, formation of H + 2 is more than twice as likely to occur from the lighter water isotopologue H2O + than D + 2 from D2O +. These findings are consistent with the ground state dissociation mechanism in which a fast projection of the ground state nuclear wave function onto the vibrational continuum of the cation potential energy surface is sometimes followed by H + 2 formation.

Strong-field-induced bond rearrangement in triatomic molecules

“…Despite the differences in the structure and bonding of the molecules, and the observed differences in the angular distributions of the bond rearrangement fragments discussed above, the bond rearrangement branching ratios in double ionization are all within an order of magnitude of each other. This is consistent with previous measurements of similar branching ratios in water [30] and even acetylene [28], where the H + 2 + C + 2 channel was estimated to be 0.05% of the dominant ion-pair channel, H + + C 2 H + . Theoretical treatment may reveal if the similarity in the branching ratios is just a coincidence or if there is a general predisposition for bond rearrangement involving two atoms located at the edges of a small molecule to occur at this level.…”

“…This qualitative argument can also explain why SO + is less likely to form from OCS than O + 2 is from CO 2 , since the sulfur atom is double the oxygen mass. Similar isotopic trends were observed in studies of bond rearrangement in methane, ammonia and water [7,30].…”

“…Bond rearrangement in water has been the subject of a variety of studies using ion [30,102,103] and electron [44] impact as well as single [11,37,38,42] and multiple photon absorption [5,22,43,52]. Oxygen core excitation via synchrotron radiation [11,37,38,42] suggests that the stimulation of bending motion, or a combination of bending and symmetric stretch modes, enhances the production of H + 2 .…”

“…The process leading to the formation of H + 2 is thought to be rapid in these situations, as short as 10 fs on the dication surface [11,42]. While fast ion impact predominantly interacts with valence, rather than core electrons, the bond rearrangement process appears to be explained by a rapid process in these cases as well, specifically a vertical ionization to the dication leading to a small probability of reaching the H + 2 + O + dissociation limit [2,30,44].…”

“…Despite the increasing attention devoted to these processes, so far most studies have focused on a single molecular species and have occurred under an assortment of experimental conditions. For example, the initiating ioniza-tion mechanism in previous bond rearrangement studies has variously included single [8,11,[37][38][39][40][41][42] and multiple photons [5,22,26,27,43] as well as electron [23,28,44] and heavy ion impact [2,7,30]. To assist in understanding these dynamics we examine bond rearrangement following ultrafast strong-field double ionization of three triatomic molecules: carbon dioxide, carbonyl sulfide and water.…”