Knowledge Bank

The potential energy surface for the internal rotation of the two methyl groups in dimethyl ether was determined by ab initio methods. For this purpose the energies of conveniently chosen conformations were calculated at the RHF level with different basis sets and corrections for electron correlations and full optimization of the geometry. The energy values were fitted to a symmetry adapted double Fourier expansion in seven terms. The rotational solutions were developed on the basis of the nonrigid point group $G36$, which factorizes the Hamiltonian matrix into 16 boxes. From the eigenvalues and eigenfunctions the far infrared spectrum was deduced. Intensities were obtained from the calculated electric dipole moments. The intensity distributions appear to reproduce the observed patterns in the fundamental and first sequence bands.