THE MICROWAVE SPECTRUM OF THE OPEN-SHELL COMPLEX $Xe-NO_{2}$

Abstract

The microwave spectrum of the $Xe-NO_{2}$ open-shell complex has been measured for the $K_{A}=0$ states using a pulsed Fourier transform microwave spectrometer between 6 and 18 GHz. We were able to study the interaction of the radical with its closed shell partner; which is expected to be intermediate between chemical bonding, where there is redistribution of electrons between the interacting species, and long range physical bonding, like that found between two closed-shell partners. With the high resolution afforded by microwave spectroscopy we were able to investigate in detail the rotational transitions of several isotopic forms of xenon within the complex, and the associated fine, magnetic hyperfine and electric quadrupole structure. Also, we were able to observe additional hyperfine structure due to the nuclear spins possessed by the xenon nuclei in the $^{129}Xe$ and $^{131}Xe$ isotopic forms of the complex. The data have been fitted to a semi-rigid Hamiltonian and used to determine a number of fine and hyperfine parameters for this state. These parameters have been used to deduce the geometry of the complex and also to investigate the possibility of electronic reorganisation between the two partners on complexation. The fine structure parameters of the complex were analysed in terms of those of the free $NO_{2}$ radical. Changes in the parameters upon complexation can be caused by a geometric effect due to rotation of the inertial axes from monomer to complex, and an electronic effect caused by a distortion of the electronic wave function on complex formation. Electronic changes may be indicative of incipient chemical bond formation. A comparison between the electronic and geometric structure of $Xe-NO_{2}$ and $Ar-NO_{2}^{1}$ will also be made.