Force field and vibrational assignment for cyclobutane from a combination of ab initio calculations and experimental data

Abstract

The geometry, force constants and dipole moment derivatives for cyclobutane have been calculated ab initio at the Hartree—Fock level using a 4–21 Gaussian basis set and the gradient method. To account for systematic deviations, the calculated force constants are scaled first and the assignment of the fundamental frequencies of cyclobutane-d 0 and -d 8 is analysed. Besides some minor reassignments, the A 1 rocking fundamentals are assigned to significantly higher frequencies than previously. The final refined force field is determined by optimizing the scale factors on the experimental frequencies.