Gas-phase Raman spectra of s-trans- and s-gauche-1,3-butadiene and their deuterated isotopologues.

The gas-phase Raman spectra of 1,3-butadiene and its 2,3-d(2),1,1,4,4-d(4) and d(6) isotopologues have been recorded using intense (6 W) green laser excitation and sensitive CCD detection. Hundreds of bands have been observed and assigned for each isotopologue. These spectra provide the best data to date for the s-trans conformer and also provide the first direct observation of the gas-phase Raman bands of the s-gauche conformer. Spectra recorded at elevated temperatures up to 250 °C for the d(0) and d(6) species help confirm the assignment of bands for the gauche rotamer. DFT computations were utilized to complement the studies. For the most part, the observed gas-phase gauche bands are in good agreement with previous matrix isolation studies. A best set of frequencies are reported for the fundamentals of the gauche rotamer of the d(0) and d(6) species.