Photoelectron spectroscopy of small antimony cluster anions: Sb-, Sb2-, Sb3-, and Sb4-

We report the 351 nm photoelectron spectra of Sb-, Sb,, Sb,, and Sb,. The electron affinity of atomic Sb is measured to be 1.046(5) eV. The Sb, photoelectron spectrum displays rich vibrational and electronic structure. Low-lying electronically excited states are observed for both the anion and the neutral. Several features in both the 351 and 364 nm photoelectron spectra of Sb, cannot be explained as Franck-Condon processes, indicating that we are accessing autodetaching resonances of the negative ion at these wavelengths. The adiabatic electron affinity of Sba is determined to be 1.282 (8) eV. For the photoelectron spectra of Sb, and Sb,, the observed electronic structure is explained in terms of recently reported ab initio calculations. The adiabatic electron affinity of Sb, is estimated to be 1.85( 3) eV, and an upper bound on the electron affinity of Sb, is reported, EA(SbJ < l.OO( 10) eV. The vertical detachment energies of Sb, and Sb, to the neutral ground states are determined to be 1.90(2) and 1.57( 5) eV, respectively. We report photoelectron angular distributions for all the observed spectra, and find that the autodetaching resonance causes unusual angular distributions for Sb, photodetachment. Finally, electron affinity trends for group V atoms, dimers, and small clusters are discussed in light of the present study.