[en] Low energy eleAsF²-tron 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 ΔH/subf/(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: ΔH/subf/(AsCl^-) =-2.2 kcal mole^-1 and ΔH/subf/(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*/sub el/(AsBr) >0.6 eV and E*/sub el/(AsCl) =2.5 eV