We report a temperature-dependent photoelectron spectroscopy study of CAl3Si- and CAl3Ge-, the first penta-atomic planar-carbon molecules characterized in both their anionic and neutral states, Significantly improved spectra were obtained under cold experimental conditions, allowing us to determine the electron affinities of CAl3Si (2.77 eV) and CAl3Ge (2.70 eV) for the first time. Three photon energies were used and the 193-nm spectra revealed two additional detachment features, allowing a total of six detachment channels to be observed for each anion. The measured vertical detachment energies and electron affinities were compared with the previous theoretical predictions, and excellent agreement was observed. (C) 2002 Elsevier Science B.V. All rights reserved.