DISCOVERY OF DATIVE BONDING OF BERYLLIUM FLUORIDE ANION BY PHOTOELECTRON VELOCITY MAP IMAGING SPECTROSCOPY

Beryllium can exhibit unusually strong attractive interactions under conditions where it is nominally a closed-shell atom. Two prominent examples are the Be$_{2}$ dimer and the He-BeO complex. Most recently, we examined the bonding of a similarly interesting molecule, the closed-shell Be-F$^{-}$ anion. This molecule preserves the closed-shell character of the atoms as the electron affinity of F is high (328.16 kJ mol$^{-1}$) while that of Be is negative. Photoelectron velocity map imaging spectroscopy, in conjunction with coupled cluster electronic structure calculations, were used to determine the vibrational frequency for BeF$^{-}$ and the electron affinity of BeF (approximately 8700 \wn). The latter has been used to determine a lower bound of 28480 \wn (343 kJ mol$^{-1}$) for the bond energy of BeF$^{-}$. The electronic structure calculations yielded predictions that were in good agreement with the observed data. A natural bond orbital analysis shows that BeF$^{-}$ is primarily bound by a dative interaction