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, ${\mathrm{P}}_2^{-}$ , and ${\mathrm{P}}_3^{-}$ formed by dissociative resonance capture of P₄. The following thermochemical values (all in kcal mole⁻¹) have been obtained: ${\mathrm{\Delta \; H\; °}}_{\text{f,298}}\mathrm{\hspace{0.17em}(}{\mathrm{P}}_2^{-}\text{)\hspace{0.17em}=\hspace{0.17em}37.2 ± 4.8;\hspace{0.17em}}\mathrm{E.A}\mathrm{.\; (}{\mathrm{P}}_2\text{) = 5.5 ± 5.3}$ ; and ${\mathrm{\Delta \; H°}}_{\text{f,298}}\mathrm{\hspace{0.17em}(}{\mathrm{P}}_3^{-}\text{)\hspace{0.17em}=\hspace{0.17em}38.2 ± 4.5}$ . 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.