Knowledge Bank

Several vibronic bands of the B-X transition of $Na3$ were investigated at rotational resolution by using resonant two photon ionization spectroscopy. The bands derive from the lowest vibrational state in the $Na3$ ground state with the vibrational temperature being around 10K. The $Na3$ B state is believed to be floppy altering its geometry in a pseudorotational motion. The vibronic states are labeled by u, the quantum number for the oscillation of the distortion amplitude and j, the quantum number for the pseudorotational motion. Our measurements include transitions into vibronic levels of the B state with $u=0$, 1 and 2 for the four lowest j's. As the rotational spectra are extremely congested even at low temperatures, OODR experiments were performed in order to label lines which share a common ground state level. For states with $j=0$ both the ground and excited state were approximated best by a rigid asymmetric top: an obtuse triangle with bond angle $\alpha =80\circ$ and bond length $r=3.25${\AA} for the ground state and an acute triangle with bond angle $\alpha =47\circ$ and bond length $r=4.05${\AA} for the B state. For states with $j\ge 1$ which exhibit a fast pseudorotational motion the time averaged geometry appears to be that of an equilateral triangle of about $r=3.75${\AA}. Strong Coriolis interaction is reflected in the structure of these bands.