The A1Σu+ system of Mg2

The A 1 Σ u + -X 1 Σ g + UV spectrum of Mg2 has been investigated with high resolution employing Fourier-transform spectroscopy and laser excitation. Computer simulation and fit of line positions to the overlapping structures in the spectra yield precise transition frequencies. Starting with the well characterized ground state X 1 Σ g + from former work, we derived excited energy levels and report on the evaluation of the A 1 Σ u + excited state, which is found to interact with another electronic state, which we identify as the lower part of the (1)1 Π u state. A coupled channels fit to the level energies of the upper state yields a reliable potential energy curve for the A 1 Σ u + state for the range of vibrational levels 1 ≤ v′ ≤ 46. A potential energy curve for the (1)1 Π u state is proposed, but the (1)1 Π u state is only characterized by its coupling to the A state, and no direct transition to a level of the (1)1 Π u state could be uniquely identified due to the overlapping spectral structures.