Reactions of ions in excited electronic states: (N2+·)* + N2 → N3++N

The formation of ${\mathrm{N}}_3^{+}$ ions from ${\mathrm{N}}_2^{\mathrm{+·}}$ ions in an excited electronic state has been studied using ion cyclotron resonance (ICR) spectroscopy. By analysis of the ICR data is was possible to determine the rate constant for formation of ${\mathrm{N}}_3^{+}$ to be k₃ = 5.5±1.0×10⁻¹¹ cm³ sec⁻¹·molecule⁻¹, the lifetime of the precursor ${\mathrm{N}}_2^{\mathrm{+·}}$ excited state to be 1/k₄>10⁻² sec, and the ratio of active ${\mathrm{N}}_2^{\mathrm{+·}}$ excited states to the remainder of the ${\mathrm{N}}_2^{\mathrm{+·}}$ formed in the electron beam to be k₂/k₁ = 10±1×10⁻³. Comparison with previously published single source work and with optical studies of Holland and Maier indicate that at least two excited states of ${\mathrm{N}}_2^{\mathrm{+·}}$ may be responsible for the formation of ${\mathrm{N}}_3^{+}$ in the single source instruments, the A ²Π state (τ ≃ 6×10⁻⁶ sec) and a quartet state (τ ≥ 10⁻² sec). The onset of ${\mathrm{N}}_3^{+}$ formation in the ICR is at 22.6±0.6 eV, about 1.5 eV above the onset in the single source mass spectrometer. It is suggested the ICR onset corresponds to the onset of the active quartet state and the mass spectrometer onset to the thermodynamical onset of the ${\mathrm{N}}_3^{+}$ ion. This analysis yields ${\mathrm{\Delta \; H}}_f\mathrm{\hspace{0.17em}(}{\mathrm{N}}_3^{+}\text{)=372± 4\hspace{0.17em}}\mathrm{kcal}/\mathrm{mole}$ .