Knowledge Bank

Rotational transistions in the microwave region have been assigned for the ground and one excited vibrational state of $CH3PF2$. From a fit of a-type Q and R-branch transitions the rotational constants for the ground state are found to be A = 7155.34 MHz, B = 6815.25 MHz, and C = 4634.54 MHz. From an analysis of the Stark effect the dipolemoment components and total dipole moment have been determined to be $\mu a=2.04$ D, $\mu b=0.21$ D, and $\mu =2.05$ D. The absence of splittings in the ground state transitions indicates that the barrier to internal rotation of the methyl group is in excess of 3500 cal/mole.