Multiphoton spectroscopy of NO?Rg (Rg = rare gas) van der Waals systems

Abstract

The spectroscopic characterization of the electronic ground and excited state interactions of NO with different rare gases is reviewed. In its electronic ground state, the NO molecule continues to serve as one of the most important benchmark systems for investigating van der Waals interactions involving open shell molecules. Combining high resolution infrared excitation with resonance enhanced multiphoton ionization (REMPI) detection, bound intermolecular bend-stretch levels have been detected for the complexes NO-Ar and NO-Ne for the first time. In parallel with these new experimental advances, new high-level ab-initio potential energy surfaces have been calculated very recently for several NO-Rg (Rg = rare gas) systems. Predictions for the bound states based on these potentials are in excellent agreement with the high resolution infrared spectra for NO-Ar and NO- Ne, demonstrating the great accuracy achieved with current ab initio methods. The large number of excited electronic states of NO provides ideal opportunities for studying molecular interactions in different excited states. The low lying Rydberg states are especially interesting because the Rydberg electron can reside in an orbital whose size is comparable with or larger than the van der Waals radius of the complexed atom. The existing set of experimental data on Rydberg states with n = 3(l = 0, 1, 2) and n = 4(l = 0) are reviewed critically. The excited states have been investigated employing mainly REMPI spectroscopy. The data provide detailed information about the bound levels of the associated intermolecular surfaces. Most of the work has concentrated on the complexes with Ar and Ne. Additional data for the states Ã2