THE 3-DIMENSIONAL POTENTIAL-ENERGY SURFACE FOR THE RING-PUCKERING, RING-DEFORMATION, AND SIH2 ROCKING VIBRATIONS OF 1,3-DISILACYCLOBUTANE
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The mid-infrared and Raman combination and hot band spectra involving the ring-puckering (22), ring-deformation (6), and SiH2in-phase rocking (21) vibrations have been analyzed for 1,3-disilacyclobutane in order to determine the ring-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 ring-deformation excited state. The parameters of the three-dimensional potential energy function V=a1x14+b1x12+b2x22+b3x32+c12x12x22+c13x12x32, where the subscripts 1, 2, and 3 refer to 22, 6, and 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 three-dimensional calculation were determined by first solving the one-dimensional problem in x1and multiplying the resulting eigenfunctions by harmonic oscillator functions in x2and x3. An excellent correspondence between the calculated and observed frequencies was obtained. The potential surface, which has a barrier to ring inversion of 81 cm-1and a minimum corresponding to a dihedral angle of puckering of 24.2 provides an accurate representation of the coupling between the puckering and the other two modes. The c12constant is negative, indicating that 22and 6are cooperative modes; c13is positive, showing that the simultaneous vibration of 22and 21results in a higher potential energy. 1982 American Institute of Physics.
