Negative ion electron impact studies of arsenic trihalides: AsF3, AsCl3, and AsBr3

Low energy electron impact of AsF3, AsCl3, and AsBr3 gases gave many ions by dissociative resonance capture. Appearance potentials have been determined by deconvolution of the capture curves, and translational energies of the majority of the ions have been measured through the resonance processes. The X− ions are formed along with electronically excited neutral AsX2, and the results allow the electronic transition energies to be determined: 7.3, 4.3, and 2.6 eV for AsF2, AsCl2, and AsBr2, respectively. From the processes giving AsX−2+X, the experimental data allow the heats of formation of the negative ions ΔHf(AsX−2) to be derived: −129.7, −65.3, and −72.5 kcal mole−1 for AsF−2, AsCl−2, and AsBr−2, respectively. The ions AsCl− and AsBr− appear to be formed along with electronically excited X2 neutral: ΔHf(AsCl−) =−2.2 kcal mole−1 and ΔHf(AsBr−) =1.7 kcal mole−1 are derived. The ions X−2 appear to be formed with electronically excited AsX neutral, allowing the electronic transition energies to be derived: E*el(AsBr) ≳0.6 eV and E*el(AsCl) =2.5 eV.