Electronic structure of B-2: theoretical and experimental results

Potential energy curves and electronic transition moments for Be-2 were cal culated using MRSDCI and EOM coupled cluster levels of theory with a (12s6p 3d2f1g)/[5s4p3d2f1g] basis set. The properties of low-lying singlet, triple t, and quintet states were predicted. MRSDCI results were found to be in ag reement 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 stat es of Be-2 were examined using laser excitation techniques. The dimer was f ormed by pulsed laser ablating Be vapor into a free-jet expansion. Disperse d fluorescence spectra were recorded following excitation of various vibrat ional 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 c m(-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 reserve d.