THE B STATE OF THE SODIUM TRIMER: PSEUDOROTATION, ROTATION, AND CORIOLIES INTERRACTION
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Date
1994
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Ohio State University
Abstract
Due to a pseudo-Jahn-Teller interaction of a $^{2}E^{\prime}$ and a $^{2}A_{1}^{\prime}$ state, the lowest potential surface of the B state of $Na_{3}$ allows for an almost free pseudorotational motion of the three Na nuclei. In this talk, a summary of the results from resonant two photon ionization and optical-optical double resonance spectroscopy of the B-X system is given. In the $X^{2}B_{2}$ ground state the molecule has a geometry of an obtuse isosceles triangle, while the $B^{2}A_{1}$ rotational structure reflects an unusual behavior: vibronic states with no excitation of the pseudoratational motion, i. e. vibronic angular momentum j=0, indicate shallow minima of the potential surface for an acute triangular shape with $48^{\circ}$ bond angle and r = 4.02(3) {\AA} bond length. The ``equivalent” equilateral triangle would have r = 3.76(5) {\AA}. States with $j \geq 1$ are pseudorotating with a time constant $\tau < 4ps$, are approximated best by an equilateral triangle with r=3.74(5) {\AA} and show a large coriolies splitting of the rotational levels which is described by a term $ \pm 2C \zeta K, C$ being the rotational constant about the rotational axis of the molecule perpendicular to the plane of the triangle, K the corresponding rotational quantum number and $\zeta$ an effective coriolis coupling constant. Moreover, an effective spin-rotation coupling parameter $y \approx 0.02 cm^{-1}$ had to be introduced which mainly accounts for the interaction with the nearby $^{2}E^{\prime}$ state.
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Author Institution: Department of Physics, The Pensylvania State University