Spectroscopic studies of gas-phase CH(D)–Ar complexes

Abstract

Van der Waals complexes formed by a labile radical and a rare-gas atom provide a means for understanding the collisional dynamics and structure of weakly bound systems.1 By comparison to their closed-shell counterparts only a few such systems have been observed and characterized. In this summary, results of experimental and modeling studies on CH(D)-Ar complexes are reported. The complexes are formed in a supersonic jet and detected by laser-induced fluorescence in the region of CH B2Σ− − X2Πr (1,0) and (0,0) bands and CD (1,0) band. The excitation spectra reveal a number of ro-vibronic bands which are assigned to various stretching and/or bending motions of the complexes. From the spectra, lower limits of the ground and excited state binding energies are estimated. Rotational analysis of eight of the CH-Ar bands yields an average ground state value of B″av = 0.174 cm−1 and excited state constants ranging from B′ = 0.086 - 0.116 cm−1. The CD-Ar bands were also analyzed and the results will be presented and discussed. The rovibronic structure of the bands has been analyzed using a model based on hindered rotation which describes the interaction of a CH(D) monomer with an Ar('S0) atom. From this model the equilibrium geometry of the ground and excited states of these complexes is inferred. These results will also be presented and discussed.