Spectroscopic characterization of the excited valence MgXe(3dδ 3Δ1), MgXe(3dπ 3Π), and MgXe(“3dσ” 3Σ+) van der Waals states

Abstract

The Mg(3s3dσ 3DJ)⋅Xe(3Σ+), Mg(3s3dπ 3DJ)⋅Xe(3Π0+,0−), and Mg(3s3dδ 3DJ)⋅Xe(3Δ1) excited states have been characterized via resonance enhanced two-photon ionization (R2PI) spectroscopy of transitions from the long-lived Mg(3s3pπ 3PJ)⋅Xe(3Π0+,0−), metastable states of the MgXe van der Waals molecule. Because the excited Mg(3d) orbital is quite diffuse and the Xe atom can approach along the nodal axis of the aligned 3d orbital, minimizing repulsion, the MgXe(3s3dδ 3Δ1) state (Do=3160±150 cm−1) is even more strongly bound than the MgXe+ core ion (for which Do=2848±150 cm−1). The MgXe(3dσ 3Σ+) state (Do=1262±150 cm−1) and the MgXe(3dπ 3Π0−) state (Do=1229±150 cm−1) are much less bound. However, the potential curves of these two states are quite different, and it is suggested that the MgXe(“3dσ” 3Σ+) state is bound only because of substantial mixing of Mg(4pσ) Rydberg character into the wave function. Interesting spin–orbit and spin–spin effects, detected and analyzed from the rotational structure of the vibrational bands, are attributed to mixing of some Xe character into molecular orbitals nominally of Mg* excited state character.