High temperature negative ions. Electron impact study of tetratomic phosphorus vapor

Appearance potentials and ion translational energies have been measured for the negative ions P, P2−, and P3− formed by dissociative resonance capture of P4. The following thermochemical values (all in kcal mole−1) have been obtained: Δ H °f,298 (P2−) = 37.2 ± 4.8; E.A. (P2) = 5.5 ± 5.3; and Δ H°f,298 (P3−) = 38.2 ± 4.5. The P− ion appears to be formed in its first excited state on low-energy electron impact of P4, and the derived heat of formation of P3, ΔH°f,298 (P3,g) =59.4±4.0, is proposed. The measurement of the increase in translational energy across resonance gave α (where α serves as the fraction of the oscillators in the transition complex which are effective for the distribution of the excess energy) = 0.43 for the three processes studied.