Integer Quantization of the Pseudorotational Motion inNa3B

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 $2\pi$ rotation in the vibrational coordinates. The $B$ state of ${\mathrm{Na}}_3$ was believed to exhibit this behavior. High resolution spectroscopy of the $B-X$ system of ${\mathrm{Na}}_3$ is reported which is reassigned as $B^2{A}_1^{\prime }-X^2{B}_2$. 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.