ROVIBRONIC ENERGY LEVELS AND INTENSITIES OF ROVIBRONIC TRANSITIONS OF NONLINEAR TRIATOMIC OPEN-SHELL RARE GAS COMPLEXES

$^{1}$ Paul D. Mills, Colin M. Western, and Brian J. Howard, J. Phys. Chem. 90, 3331 (1986).Author Institution: Department of Chemistry, Emory University; Molecular Spectroscopy Division, National Bureau of StandardsThis paper is concerned with the rovibronic energy levels and intensities of rovibronic transitions in complexes formed from a rare gas atom and an open-shell diatomic molecule in a $^{2}\Pi$ or a $^{2}\Sigma$ electronic state. Previously, Mills et al, have discussed pure rotational spectra of ArNO for the $^{2}\Pi$ $case^{1}$. The model system used in this work is an ArOH Van der Waals complex, where the OH internuclear axis can be at any angle ($\theta$) relative to the line connecting the Ar atom to the center of mass of the OH. The electronic states under consideration are the $X^{2}\Pi$ and the $A^{2}\Sigma$ states of the OH radical. Such a model can be represented as an asymmetric rotor possessing electron-spin angular momentum and electronic orbital angular momentum. The components of the rotational angular momentum are most naturally defined in the principal axis system of the triatomic ArOH complex. On the other hand, the components of the electronic orbital angular momentum are most naturally defined in the H diatomic axis system. The components of the electron-spin angular momentum can be defined either in the OH axis system or in the principal axis system of ArOH. We have derived matrix elements of the total rovibronic Hamiltonian, taking into account, as did Mills $et al.^{1}$, the spin-orbit coupling, the spin-rotation interaction, and a quenching parameter, which allows the degeneracy of the $\Pi_{x}$ and $\Pi_{y}$ orbitals existing in the diatomic radical to be split upon complex formation. We have also derived the electronic dipole transition moment matrix elements for rovibronic transitions of the type $^{2}\Pi \leftrightarrow ^{2}\Pi$ and $a ^{2}\Pi \leftrightarrow ^{2}\Sigma$ respectively, where the $^{2}\Pi$ and $^{2}\Sigma$ labels describe electronic states in the diatomic radical. Results of calculations show that the ``goodness'' of various quantum numbers and the type of the rovibronic transitions (a,b or c-type) depend on the angle ($\theta$). Both the theory and examples of calculated spectra with different values of the various parameters will be presented