Knowledge Bank

The lowest rotational transitions $J=1+0$ of $NaBH4$ and $KBH4$ were observed using a Fourier transform microwave spectrometer combined with the laser ablation method. This method was proved useful for studying molecules which easily react with metal and thus are different to produce by a conventional jet nozzle made of metal. The hyperfine structure was resolved and the eQq constants of both the alkali metal and boron atoms were determined. The values of eQq obtained for the alkali metal atoms are close to those for NaCl and KCl, indicating that $NaBH4$ and $KBH4$ have ionic structures. No splittings due to the internal rotation of $BH4$ were observed in our FIMW spectra of $NaBH4$ and $KBH4$.