Geometric and electronic structures of Al4P-, Al4P, Ga4P- and Ga4P are studied using B3LYP-DFT and CCSD(T) methods with the 6-311+G(2d) and 6-311+G(2df) one-particle basis sets. The anions have similar square pyramidal (C-4 nu) gas phase equilibrium geometry while the neutral species possess the trapezium (C-2v) planar geometry in accordance with the predictions of Boldyrev and Wang [A.I. Boldyrev, L.S. Wang, J. Phys. Chem. A 105 (2001) 10759]. Electron detachment processes from the ground electronic states of the anions are presented and an attempt is made to assign the features observed in the anion photoelectron spectra of Al4P- and Ga4P-. (c) 2005 Elsevier B.V. All rights reserved.