VARIATIONAL CALCULATIONS FOR THE ROVIBRATIONAL STATES OF (SI2C)-C-12 AND (SI2C)-C-13

Rovibrational states of the ground electronic state of (Si2C)-C-12 and (Si2C)-C-13 isotopomers have been calculated variationally. The poten tial energy surface used in the calculations was obtained from an MP2/ TZ2Pf ab initio surface of Barone et al. (V. Barone, P. Jensen and C. Minichino, J. Mol. Spectrosc, 154 (1992) 252) by applying the restrict ions of 100 degrees less than or equal to alpha < 150 degrees. The ab initio surface was refitted to a fourth-order polynomial with an Ogilv ie-Tipping variable using a multi-dimensional least-squares procedure. The force field was then embedded in an Eckart-Watson vibration-rotat ion Hamiltonian, from which low-lying vibrational states and rovibrati onal states of (Si2C)-C-12 and (Si2C)-C-13 were obtained. The calculat ed vibrational states (100) and (001) of (Si2C)-C-12 and the C-13 isot opic shifts agree well with a recent experiment (J.D. Presilla-Marquez and W.R.M. Graham, J. Chem. Phys., 95 (1991) 5612). Also, the calcula tions support the vibrational transition at 658.2 cm(-1) found by Kafa fi et al. (Z.H. Kafafi, R.H. Hauge, L. Fredin and J.L. Margrave, J. Ch em. Phys., 87 (1983) 797). The rotational energies of these isotopomer s for the lowest six vibrational states are given as are the rotationa l constants for (Si2C)-C-12 and (S2C)-C-13.