Knowledge Bank

The spectrum of the ground torsional state of dimethyl ether has been measured in the frequency range 100. 600 GHz covering rotational states up to $J=25$ and $K=5$. Over 700 torsional splittings from -250 rotational lines were analyzed using a PAM Hamiltonian. A total of 4 parameters were varied in a least squares fit using higher order Van Vleck perturbation terms. The free parameters included the torsional barrier, $V3$, independent a- and b-type rotation-torsion interaction parameters $Qa$ and $Qb$, and the C rotational constant. The RMS of the fit was . Because of the parameterization of the Hamiltonian, this method should be applicable to other internal rotor molecules of this symmetry.