Photoelectron spectroscopy of As−,As2−,As3−,As4−, and As5−

The negative ion photoelectron spectra of As−, As2−, As3−, As4−, and As5− have been measured. From these, the electron affinities of As, As2, As3, As4, and As5 have been determined to be 0.814, 0.739, 1.45, <0.8, and ∼1.7 eV, respectively. In the case of As2−, the following molecular constants were also determined: re(As2−)=2.239 A, ωe(As2−)=293 cm−1, ωeχe(As2−)=4.9 cm−1, D0(As2−)=3.89 eV, and ΔE[2Πg(3/2)−2Πg(1/2)]=0.256 eV. In the case of As3−, vertical detachment energy (VDE) was measured to be 1.62 eV, and for As3, ΔE(2A2−2B1) was determined to be 0.36 eV. For As4−, VDE was found to be 1.52 eV. The relatively high stability of As5− suggests that it, like P5−, may be a candidate for forming cluster-assembled, ionic crystals of stoichiometry, MAs5, where M is an alkali metal atom. Similiarities with other small cluster anions of Group V elements are also discussed.