Observation of stable HO${}_4$${}^{+}$ and DO${}_4$${}^{+}$ ions from ion-molecule reactions in helium nanodroplets

Abstract

Ion-molecule reactions between clusters of H${}_2$/D${}_2$ and O${}_2$ in liquid helium nanodroplets were initiated by electron-induced ionization (at 70 eV). Reaction products were detected by mass spectrometry and can be explained by a primary reaction channel involving proton transfer from H${}_3$${}^{+}$ or H${}_3$${}^{+}$(H${}_2$)${}_n$ clusters and their deuterated equivalents. Very little HO${}_2$${}^{+}$ is seen from the reaction of H${}_3$${}^{+}$ with O${}_2$, which is attributed to an efficient secondary reaction between HO${}_2$${}^{+}$ and H${}_2$. On the other hand HO${}_4$${}^{+}$ is the most abundant product from the reaction of H${}_3$${}^{+}$ with oxygen dimer, (O${}_2$)${}_2$. The experimental data suggest that HO${}_4$${}^{+}$ is a particularly stable ion and this is consistent with recent theoretical studies of this ion.

16 pages, 3 figures