Photoelectron Velocity Map Imaging Spectroscopy of the Beryllium Trimer and Tetramer.

Computational studies of small beryllium clusters (BeN) predict dramatic, nonmonotonic changes in the bonding mechanisms and per-atom cohesion energies with increasing N. To date, experimental tests of these quantum chemistry models are lacking for all but the Be2 molecule. In the present study, we report spectroscopic data for Be3 and Be4 obtained via anion photodetachment spectroscopy. The trimer is predicted to have D3h symmetric equilibrium structures for both the neutral molecule and the anion. Photodetachment spectra reveal transitions that originate from the X2A2″ ground state and the 12A1' electronically excited state. The state symmetries were assigned on the basis of anisotropic photoelectron angular distributions. The neutral and anionic forms of Be4 are predicted to be tetrahedral. Franck-Condon diagonal photodetachment was observed with a photoelectron angular distribution consistent with the expected Be4-X2A1 → Be4X1A1 transition. The electron affinities of Be3 and Be4 were determined to be 11363 ± 60 and 13052 ± 50 cm-1, respectively.

Characterization of the Ground States of BeC2 and BeC2- via Photoelectron Velocity Map Imaging Spectroscopy.

Due to their potentially unique properties, beryllium carbide materials have been the subject of many theoretical studies. However, experimental validation has been lacking due to the difficulties of working with Be. Neutral beryllium dicarbide has been predicted to have a T-shaped equilibrium structure (C2v), while previous quantum chemistry calculations for the structure of the anion had not yielded consistent results. In this study, we report photoelectron velocity map imaging spectra for the BeC2- X 2A1 → BeC2 X 1A1 transition. These data provide vibrational frequencies and the electron affinity of BeC2. Ab initio electronic structure calculations, validated against the experimental data, show that both the anion and the neutral form have C2v equilibrium geometries with polar covalent bonding between Be and the C2 subunit. Computed vibrational frequencies and the electron affinity, obtained at the CCSD(T) level of theory, were found to be in good agreement with the measurements.