Spectroscopic characterization of Be2+ X 2Σu+ and the ionization energy of Be2

Rotationally resolved spectra for Be-2(+) have been recorded using the pulsed-field ionization zero kinetic energy photoelectron technique. Vibrational levels in the range v(+)=0-6 were observed. The rotational selection rules confirmed that the ground state is (2)Sigma(+)(u), resulting from the removal of an electron from the sigma(u) antibonding orbital of Be-2. The bond energy and equilibrium distance for Be-2(+) were found to be D-e(+)= 16 438(5) cm(-1) and R-e(+)=2.211(8) angstrom. The ionization energy for Be-2 [59 824(2) cm(-1)] was also refined by these measurements. Comparisons with high-level theoretical results indicate that the bonding in Be-2(+) is adequately described by multi reference singles and doubles configuration interaction (MRDCI) calculations that employ moderate to large scale basis sets. (C) 2010 American Institute of Physics. [doi:10.1063/1.3472977]