Integer quantization of the pseudorotational motion in Na3 B.

Abstract

Fractional quantization of vibronic states of a molecule can be expected when two electronic potential energy surfaces experience a conical intersection and the vibrational and electronic wave functions change sign under $2\ensuremath{\pi}$ rotation in the vibrational coordinates. The $B$ state of ${\mathrm{Na}}_{3}$ was believed to exhibit this behavior. High resolution spectroscopy of the $B\ensuremath{-}X$ system of ${\mathrm{Na}}_{3}$ is reported which is reassigned as ${B}^{2}{A}_{1}^{\ensuremath{'}}\ensuremath{-}{X}^{2}{B}_{2}$. The analysis of rotational structure and Coriolis interaction shows that the vibronic angular momentum j is integer quantized, in contrast to previous interpretations. Therefore, the $B$ state of ${\mathrm{Na}}_{3}$ can no longer be considered as an example of Berry's geometrical phase in a molecule.