Internal motion in MBH4

The internal motion in MBH 4 , with M denoting an alkali atom, has been discussed theoretically by taking into account two internal degrees of freedom, the M-(BH 4 ) stretch and the BH 4 internal rotation, in addition to the overall rotation. The energy level expressions were derived to discuss characteristic features of the rotational spectra in the ground as well as in excited vibrational states. Particular attention was paid to splittings in the rotational spectra which are caused by the tunneling motion of the BH 4 group.