Evidence for a non-Rydberg molecular doubly excited state of Ca2

We report experimental and theoretical evidence of a non-Rydberg molecular doubly excited state of Ca2 involving excited molecular orbitals mixing 4p and 3d characters. The excitation spectrum of Ca2, carried by helium or argon clusters, is recorded experimentally in the range 25 600–27 800 cm−1, displaying a bimodal structure. The latter is interpreted from ab initio calculation and analysis of the adiabatic states of Ca2 up to doubly excited asymptotes Ca(4p3d1D) + Ca(4s21S) and Ca(4s3d3D) + Ca(4s4p3P), and the relevant dipole transition moments. The bimodal structure is assigned as resulting from the avoided crossing between adiabatic states 31Πu and 41Πu, reflecting the mixing of doubly excited configurations and absorbing singly excited configurations.