Spectroscopic characterization of the metastable 3pπ 3Π+,0− valence states and the 4s3Σ+ Rydberg states of the MgKr and MgXe van der Waals molecules

Abstract

The first metastable valence excited states and the first Rydberg states of the MgKr and MgXe molecules have been characterized by resonance two-photon photoionization (R2PI) spectroscopy. The Mg(3s3p 3PJ)⋅RG(3Π0+,0−) metastable states, produced by expanding the products of a laser-ablated magnesium rod in Kr/Ar or Xe/Ar gas mixtures into a supersonic expansion, were excited by a dye laser pulse to several vibrational levels of the Mg(3s4s 3S1)⋅RG(3Σ+) Rydberg states, with detection by ionization with a second dye laser pulse. Spectroscopic constants, bond energies, and bond lengths are reported for both states of MgKr and MgXe. The Σ+3 Rydberg states are much more strongly bound than the lower Π0−3 valence states, and in fact are essentially as strongly bound as the ground states of the analogous MgRG+ ions, characterized previously in the same apparatus. This clearly indicates that the RG atoms can readily penetrate the diffuse Mg(4s) Rydberg electron cloud. The interesting and unusual spin–orbit and “spin–spin” effects observed are attributed to mixing of some RG character into wave functions of predominantly Mg* excited state character. Bonding and spin–orbit interactions in the MgAr, MgKr, and MgXe first triplet metastable and Rydberg states are discussed.