Electronic structure of B2:: theoretical and experimental results

Potential energy curves and electronic transition moments for Be-2 were calculated using MRSDCI and EOM coupled cluster levels of theory with a (12s6p3d2f1g)/[5s4p3d2f1g] basis set. The properties of low-lying singlet, triplet, and quintet states were predicted. MRSDCI results were found to be in agreement with experimental observations. Predictions for the B(1)Sigma(u)(+) - A'(1)Pi(g) transition were used to guide an experimental search for the A' state, which had not been observed previously. Low-lying electronic states of Be-2 were examined using laser excitation techniques. The dimer was formed by pulsed laser ablating Be vapor into a free-jet expansion. Dispersed fluorescence spectra were recorded following excitation of various vibrational levels of the B(1)Sigma(u)(+) state, and bands of the B(1)Sigma(u)(+) -A'(1)Pi(g) transition were observed. The term energy (T-e =13711 +/- 30 cm(-1)) and vibrational interval (Delta G(1/2) = 726 +/- 25 cm(-1)) for the A' state were determined. (C) 1999 Elsevier Science B.V. All rights reserved.