Polyatomic Ions of Helium, Neon, and Argon

The presentation of the reported research on polyatomic cations will be made analogous to the diatomic species. As shown above, atomic ions X may bind a light noble gas element with a binding energy up to 96.1 kcal/mol (ArH ). We will first ask the question how many noble gas atoms may the atomic ions X bind in polyatomic cations Ng jX . Then, we will proceed to cations which are formally formed from diatomic ions XY and He, Ne or Ar. The reader will see that the available information on polyatomic cations is well understood using this scheme and that it is possible to make an educated guess about the stability of unknown species without even performing quantum mechanical calculations. 

The reaction rates of reaction (1) have been measured for the three light noble gases but only for ArjH was the bond energy deduced as 3.82 — D(Ar2) eV [100]. Theoretical studies at the Hartree-Fock level have been reported by Matcha, Milleur and coworkers for HenH [101], Ne H [102] and Ar H  

Matcha and coworkers [105] also reported theoretical results based on Hartree-Fock SCF calculations for the mixed triatomic cation HeNeH . They 

5 kcal/mol for the loss of Ne. These numbers, which are smaller (for He loss) and larger (for Ne loss) compared with the D, values for He2H and Ne2H agree nicely with the donor-acceptor model. Ne is a better donor than He and HeH is a better acceptor than NeH which explains the calculated reaction energies. No experimental reports are known to us about mixed cations NgNg H+. 

In 1970, Clampiti and Jefferies [106] reported their molecular beam experiments for various ion clusters. For Ne Li , they found the largest peak for m = 1 followed by nearly identical signals for m = 2, 3, 4, 5, 6. The yield of ion clusters decreases abruptly beyond HcgLi . The same result was found for hydrogen clusters (H2) Li. A remarkable feature of the mass spectrum was the relative insignificance of clusters with m 6. It was concluded [106] that six molecules around an ion probably constitute a complete shell . This result is important in comparison with theoretical studies of Ng Be ions. 

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