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

Abstract

The formation of N3+ ions from N2+· 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 N3+ to be k3 = 5.5±1.0×10−11 cm3 sec−1·molecule−1, the lifetime of the precursor N2+· excited state to be 1/k4>10−2 sec, and the ratio of active N2+· excited states to the remainder of the N2+· 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 N2+· may be responsible for the formation of N3+ 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 N3+ 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 N3+ ion. This analysis yields Δ Hf (N3+)=372± 4 kcal/mole.