Dissociative ionization of the H₂O molecule bombarded by swift singly charged and slow highly charged ions

Abstract

Fragment ion energy spectra of the water molecule have been measured in conventional crossed‐beam experiments by the impact of 46 keV/u energy, singly charged ions (SCIs) and 4.3 keV/u energy, highly charged ions (HCIs). Double differential cross sections have been determined and a comparative analysis has been performed. We found that the fragmentation spectra for SCIs and HCIs are very similar, indicating that both collisions lead to the same fragmentation channels. This suggests that the Coulomb explosion of the water molecule is dominantly determined by the charge state of the transient molecular ions, and it is almost independent from the primary ionization mechanism. Differences were observed not only between the SCI and HCI impact‐induced fragmentation cross sections, but between those obtained by the 60 keV N6+ and 70 keV O7+ projectiles. The differences were attributed to the selectivity of the electron capture process for HCIs. Multiple target ionization cross sections have been deduced from the fragment ion spectra. We found contributions of up to fivefold ionization for SCIs and up to sixfold ionization for HCIs.

Anion and cation emission from water molecules after collisions with 6.6-keV 16O+ ions

“…The presently obtained energy spectra of cations show a striking difference from those obtained in collisions involving projectiles of higher charge or higher energy [25][26][27][28][29], as shown in Fig. 8.…”

“…Red squares: for 6.6-keV O + +H2O collision, present work. Open triangles: for 650-keV N + +H2O collision from [29]. Circles: for 70-keV O 7+ +H2O collision from [29].…”

“…In this section we focus on the mechanisms underlying the formation of low-energy cation fragments. Prior to this work, fragmentation of water by high-energy singly charged projectiles and low-energy highly charged ions was compared and the DDCS fragment spectra were found to be similarly structured [29]. The observed peak structures were explained by Coulomb explosion of the multiply charged target molecule left after the collision, even though the ionization mechanisms were different in the two cases.…”

“…On the contrary, multiple electron capture by highly charged ions occuring in large impact parameter collisions and multiple ionization by fast dressed projectiles imply a brief interaction with the target, so that the projectile has little influence on the Coulomb explosion of the target in these cases. The latter is true even if, according to classical trajectory model calculations (CTMC), multiple ionization induced by fast, singly charged projectiles results from close collision events at small impact parameters [29].…”

“…Other groups [10][11][12][13][14][15][16] focused investigations on the regime of lower incident energies, down to keV/nucleon and sub-keV/nucleon ranges. In this regime, measurements of absolute cross sections for fragment emission, differential in both emission energy and angle, provided further insight into the fragmentation mechanisms of Coulomb explosion and binary collisions [11][12][13][25][26][27][28][29].…”