Knowledge Bank

The torsional spectroscopic parameters of the ISO. TRANS and CIS varieties of butene determined from fully and partially optimized ab initio calculations. For this purpose the energy of conveniently chosen conformations were filled to a symmetry adapted double Fourier expansion in seven terms The band positions were calculated by solving variationally the nuclear Hamiltonian by using $G36$ symmetry eigenvectors as trial function. The spectroscopic parameters and the experimental frequencies were compared with the results obtained from RHF calculations performed with large basis set with d and f polarization orbitals and the additions of MP2 and MP4 corrections to the correlation energy. The expansion coefficients of the interaction terms in the potential surfaces are analyzed from the energies and the structural data of the nuclear conformations.