PNNL

Abstract

Samples of trans, trans and cis, cis forms of butadiene-1, 4-d2 have been synthesized and found to contain useful amounts of the cis, trans species as a contaminant. Assignments of fundamental frequencies for the three isotopomers of butadiene-1,4-d2 have been extended and improved from investigations of their Raman spectra as well as their IR spectra. High-resolution IR spectra have been recorded for the three isotopomers, and a rotational analysis has been completed for strong bands of each species. Ground state and some upper state rotational constants have been fit. Corresponding ground state moments of inertia compare faborably with equilibrium moments of inertia obtained from B3LYP/6-311++G** theory. In the absence of rotational constants for 13C isotopomers it is premature to attempt an improved structural analysis of butadiene to assess how p-electron delocalization affects structure.