DETERMINATION OF POTENTIAL BARRIERS: THE UPSIDE-DOWN RKR METHOD
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Date
1981
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Ohio State University
Abstract
Predissociation by tunnelling through a potential barrier has been observed in many diatomic molecules. These barriers may occur in the ``rotationless’’ potential, or they may result from, the contribution of the rotational kinetic energy, $K^{2}J(J+1)/2\mu R^{2}$. The breakoff of bound levels at high J has often been used to characterize the long-range part of the potential curve, through the limiting curve of dissociation. In the present study we consider the information about the potential curve that can be obtained directly from analysts of the lifetimes of the predissociated Levels. The semiclassical expression for the barrier tunnelling $probability^{1}$ contains an integral of the same from as the JWKB quantization condition for the vibrational quantum number in the bound portion of the potential. Thus we can use the observed lifetimes to derive a quantity (-$\epsilon$) that can he considered to be the vibrational quantum number in the barrier region, measured from the top of the. barrier. Alternately, we can consider the barrier turned upside-down, and use the observed energies, linewidths, and J assignments to determine harrier turning points using convential RKR methods. We will present results from application of this method to the $calculated^{2}$ quasibound levels of $HeH^{+}$, and the recently $observed^{3}$ quasibound levels in $O_{2}^{+}(f^{4}\pi_{g}$). We will also discuss the limitations that result from the observation of only a few $\nu$ levels for each .J, and suggest some ideas on how the data can be merged.
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$^{1}$ See for example R. J. LeRoy and W.-K. Liu, J. Chem. Phys. 69, 3622 (1978). $^{2}$ See R. I. Price, Chem. Phys. 31, 309 (1978). $^{3}$ H. Helm, P. C. Cosby, and D. L. Huestis, J. Chem Phys. 73, 2629 (1980).
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