A microwave study of the open-shell complex Kr–NO2

Abstract

Microwave spectra of the open-shell complex Kr–NO₂ have been recorded. Each rotational transition showed significant hyperfine structure due to fine, magnetic hyperfine and electric quadrupole interactions. The spectra could be fitted to a semi-rigid molecule Hamiltonian, but the spectra show significant evidence of large internal motion, in particular a tunnelling motion between the two equivalent non-planar structures of the complex. The spectroscopic parameters were analysed in terms of those of the monomer NO₂ to obtain a detailed structure. In particular the anisotropic hyperfine interactions provide information on the orientation of NO₂ within the complex and on electronic changes caused by distortion of the electronic wavefunction on complex formation. The Fermi contact interaction indicates little electron rearrangement at the nitrogen nucleus. However the spin–rotation constants indicate that there could be a significant rearrangement of the more diffuse electrons, rather larger than that in Ar–NO₂.