Dynamic frequency shifts in pseudorotating Na3

Abstract
ESR spectra assigned to pseudorotating Na3 molecules have been obtained by clustering atomic sodium in an argon matrix. Both a pseudorotating spectrum and the previously reported ’’stationary’’ spectrum are observed. As in the analogous potassium case, the pseudorotating spectrum is attributed to a rapid exchange between the three equivalent potential wells of a Jahn–Teller distorted trimer. The ESR spectra show an extreme alternating linewidth effect. Even at T≳30 K, only those four hyperfine (hf) components which do not broaden are observed. The relaxation matrix formalism is applied to pseudorotating Na3 and derived expressions give a good fit to the measured line positions. These show 5–10G ’’dynamic frequency shifts,’’ much larger in magnitude than normally encountered in exchanging radicals. The measured g value and hf constants for pseudorotating Na3 are in close correspondence with those predicted from the stationary trimer parameters. Together the two spectra determine the sign of the hf coupling in Na3.