Ab Initio Study of the Torsional Motion in Tolane

Accurate prediction of the torsional barrier height in tolane is achieved by systematically extrapolating to the Dunning complete basis set limit at MP2 level with a spin-component-scaled correction. The zero-point energy correction is calculated at the B98/cc-pVDZ level based on a benchmark test using the experimental data for benzene. The final calculated barrier height is 202.2 cm, in excellent agreement with the observed value. The correct barrier height enables the the vibrational energy levels and other spectroscopic properties to be determined accurately through numerical integration of the torsional Schrödinger equation. This study provides a nearly complete computational solution to the torsional problem in tolane and may aid the exploration of torsional motions in similar molecules.