Hydrogen ion cluster
A hydrogen molecular ion cluster or hydrogen cluster ion is a positively charged cluster of hydrogen molecules. The hydrogen molecular ion (H+
2) and trihydrogen ion (H+
3) are well defined molecular species. However hydrogen also forms singly charged clusters (H+
n) with n up to 120.
Hydrogen ion clusters can be formed in liquid helium or with lesser cluster size in pure hydrogen. H+
6 is far more common than higher even numbered clusters.H+
6 is stable in solid hydrogen. The positive charge is balanced by a solvated electron. It is formed when ionizing radiation impinges on solid hydrogen, and so is formed in radioactive solid tritium. In natural hydrogen treated with radiation, the positive charge transfers to HD molecules, in preference to H2, with the ultimate most stable arrangement being HD(HD)+HD.H+
6 can migrate through solid hydrogen by linking a hydrogen molecule at one end and losing it at the other: H2 + H+
6 → H+
6 + H2. This migration stops once an HD molecule is added resulting in a lower energy level. HD or D2 is added in preference over H2.
Clampitt and Gowland found clusters with an odd number of hydrogen atoms H+
3+2n and later showed that H+
15 was relatively stable. H+
3 formed the core of this cluster with six H2 molecules surrounding it. Hiroka studied the stability of the odd numbered clusters in gas up to H+
21. Bae determined that H+
15 was especially stable amongst the odd numbered clusters.
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