ANALYSIS OF TORSIONAL SPECTRA OF MOLECULES WITH 2 C3V INTERNAL ROTORS .14. CIS-2-BUTENE AND TRANS-2-BUTENE

The low frequency Raman and far infrared spectra of gaseous cis- and frans-2-butene have been recorded from 70-450 cm-1. Considerable torsional data have been obtained for the trans-2-butene molecule with the A1, torsional fundamental being observed at 163.6 cm-1 in the infrared spectrum. The overtone of the Bg fundamental was observed in the Raman spectrum at 432 cm-1. The torsional data have been used to determine the potential function based on a semirigid model and the effective barrier was found to be 713 cm-1 (2.04 kcal/mole). The cosine-cosine coupling term, V33, was found to be zero whereas the sine-sine coupling term, V33., has a value of -48 cm-1 ( -0.14 kcal/mole) and V60 = V60= -4 cm-1 ( -0.01 kcal/mole). For the cis-2-butene molecule only the B2 torsional mode was observed at 101.0 cm-1 which gives an effective barrier of 250 cm -1(0.87 kcal/mole). These data are compared to the corresponding quantities obtained earlier by other methods. © 1979 American Institute of Physics.