The threehyphen;dimensional potential energy surface for the ringhyphen;puckering, ringhyphen;deformation, and SiH2rocking vibrations of 1,3hyphen;disilacyclobutane

摘要

The midhyphen;infrared and Raman combination and hot band spectra involving the ringhyphen;puckering (ngr;22), ringhyphen;deformation (ngr;6), and SiH2inhyphen;phase rocking (ngr;21) vibrations have been analyzed for 1,3hyphen;disilacyclobutane in order to determine the ringhyphen;puckering energy levels for the ground and excited state of the other two vibrations. The puckering levels are only slightly perturbed in the rocking excited state but substantially altered in the ringhyphen;deformation excited state. The parameters of the threehyphen;dimensional potential energy functionV=a1x41+b1x21+b2x22+b3x23+c12x21x22+c13x21x2@qL3, where the subscripts 1, 2, and 3 refer to ngr;22, ngr;6, and ngr;21, respectively, were adjusted in order to obtain the best fit between the observed and calculated frequencies. For the energy level calculations, the Hamiltonian was symmetry factored into eight separate symmetry blocks. The basis functions for the threehyphen;dimensional calculation were determined by first solving the onehyphen;dimensional problem inx1and multiplying the resulting eigenfunctions by harmonic oscillator functions inx2andx3. An excellent correspondence between the calculated and observed frequencies was obtained. The potential surface, which has a barrier to ring inversion of 81 cmminus;1and a minimum corresponding to a dihedral angle of puckering of 24.2deg; provides an accurate representation of the coupling between the puckering and the other two modes. Thec12constant is negative, indicating that ngr;22and ngr;6are cooperative modes;c13is positive, showing that the simultaneous vibration of ngr;22and ngr;21results in a higher potential energy.