The ionization energy of Be2, and spectroscopic characterization of the (1)3Σ +u, (2)3Πg, and (3)3Πg states

Abstract

Low lying electronic states of the beryllium dimer were investigated by laser induced fluorescence (LIF) and resonance enhanced multiphoton ionization (REMPI) techniques. Be₂ was formed by pulsed laser ablation of Be metal in the presence of helium carrier gas, followed by a free jet expansion into vacuum. Several previously unobserved states of the dimer were characterized. These included transitions of the triplet manifold (2)³Π_g ← (1)³Σ⁺_u and (3)³Π_g ← (1)³Σ⁺_u, for which rotationally resolved bands were obtained. In addition, transitions to the v′ = 10–18 vibrational levels of the A ¹Π_u state were recorded. Photoionization efficiency (PIE) measurements were used to determine an accurate ionization energy (IE) for Be₂ of 7.418(5) eV and the term energy for (1)³Σ⁺_u. Above the ionization threshold the PIE spectrum was found to be highly structured, consisting of overlapping Rydberg series that converged on excited vibrational levels of Be₂⁺. Analysis of these series yielded a vibration frequency for the X ²Σ⁺_u state of 498(20) cm⁻¹. The bond dissociation energy for Be₂⁺, deduced from the IE measurement, was 16 072(40) cm⁻¹. Multi-reference configuration interaction (MRCI) calculations were carried out for Be₂ and Be₂⁺, yielding results that were in excellent agreement with the experimental observations.