ELECTRON-SPIN AND TUNNELING EFFUCTS IN THE MICROWAVE SPECTRUM OF $SO_{2}-O_{2}$

Author Institution: Optical Technology Division, National Institute of Standards and Technology; Faculty of Science, University of United Arab EmiratesThe rotational spectrum of the $SO_{2}--O_{2}$ complex has been recorded between 6 GHz and 24GHz using a pulsed molecular-beam Fourier-transform microwave spectrometer The spectrum is complicated by the spin of the triplet oxygen and tunneling of the two monomers within the complex. Approximately sixty {a}- and {c}-type transitions with J = 0 to 8 and $K_{a} = 0,1,2$ have been assigned and confirmed by combination differences. The observed transitions correlate to the lower ($\omega= 0$) energy component of the Ospin-spin multiplet. Transitions associated with the higher energy ($\omega = \pm 1$) component have not been assigned, presumably due to the lower population of this state in the cold molecular beam ($T_{r} = \sim 1$K). We none that in free $O_{2}$ the spin-spin splitting is approximately 4 $cm^{-1}$ (6K). The ratio of the frequencies of the two observed $\Delta K = 1$ subband origins is approximately 1.6, compared to a value of 3 expected for a rigid prolate top. A tunneling motion which reverses the sign of the c-type dipole moment component is used to explain thisanomaly. Such a tunneling motion is anticipated from previous studies on $Ar-SO_{2}$ and $SO_{2}$ dimer. A fit of the observed transitions to a rigid rotor hamiltonian with a tunneling term produces a standard deviation of 23 MHz and tunneling splitting of 2.3 GHz. This standard deviation is significantly greater than the experimental precision of $\sim 1$ kHz and is mainly attributed to the neglect of the electron spin. An alternative lit of this same data was carried out using a Hamiltonian which takes into account effects of electron spin and approximates a tunneling coefficient. This second lit produced errors on the order of1 MHz and confirms that both the electron spin and the tunneling motion must be simultaneously considered future. efforts are directed at developing a rotation-tunneling-spin Hamiltonian to model the spectrum. In addition, isotopic studies are being undertaken to determine die orientation of the $SO_{2}$ and $O_{2}$ subunits the complex