Four-body conversion of atomic helium ions

The conversion of atomic helium ions into molecular ions was studied in pure helium and in helium-neon mixtures containing between 0.1 at.% and 50 at.% neon. The experiments showed that the termolecular conversion reaction, ${\mathrm{He}}^{+}+2\mathrm{}\mathrm{He}\to \mathrm{He}_2^{}{}_{}{}^{+}+\mathrm{He}$, is augmented by the four-body conversion reaction ${\mathrm{He}}^{+}+3\mathrm{}\mathrm{He}\to \mathrm{products}$, where the products could include either $\mathrm{He}_2^{}{}_{}{}^{+}$ or $\mathrm{He}_3^{}{}_{}{}^{+}$ ions. Conversion rate coefficients of (5.7 ± 0.8) × ${10}^{-32\mathrm{}}$ ${\mathrm{cm}}^6$ ${\sec }^{-1\mathrm{}}$ and (2.6 ± 0.4) × ${10}^{-49\mathrm{}}$ ${\mathrm{cm}}^9$ ${\sec }^{-1\mathrm{}}$ were found for the termolecular and four-body conversion reactions, respectively. In addition, rate coefficients for the following ${\mathrm{Ne}}^{+}$ conversion reactions were measured: ${\mathrm{Ne}}^{+}+\mathrm{He}+\mathrm{He}\to {\left(\mathrm{HeNe}\right)}^{+}+\mathrm{He}$, (2.3 ± 0.1) × ${10}^{-32\mathrm{}}$ ${\mathrm{cm}}^6$ ${\sec }^{-1\mathrm{}}$; ${\mathrm{Ne}}^{+}+\mathrm{He}+\mathrm{Ne}\to {\left(\mathrm{HeNe}\right)}^{+}+\mathrm{Ne}$ or $\mathrm{Ne}_2^{}{}_{}{}^{+}$ + He, (8.0 ± 0.8) × ${10}^{-32\mathrm{}}$ ${\mathrm{cm}}^6$ ${\sec }^{-1\mathrm{}}$; and ${\mathrm{Ne}}^{+}+\mathrm{Ne}+\mathrm{Ne}\to \mathrm{Ne}_2^{}{}_{}{}^{+}+\mathrm{Ne}$, (5.1 ± 0.3) × ${10}^{-32\mathrm{}}$ ${\mathrm{cm}}^6$ ${\sec }^{-1\mathrm{}}$. All rate coefficients are at a gas temperature of 295 K.