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

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 signif icant evidence of large internal motion, in particular a tunnelling motion between the two equivalent non-planar structures of the complex. The spectr oscopic parameters were analysed in terms of those of the monomer NO2 to ob tain a detailed structure. In particular the anisotropic hyperfine interact ions provide information on the orientation of NO2 within the complex and o n 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 diffu se electrons, rather larger than that in Ar-NO2.