Molecular force fields of 8-trans-1,3-butadiene and the second stable conformer

Normal-coordinate analyses of s-trans-1,3-butadiene and its various deuterated and 13C-substituted analogs were performed using the group-coordinate force field, and a set of force constants was determined. The infrared spectra of the second stable conformer of 1,3-butadiene-d₀,-1,1,4,4-d ₄, and-d₆ were analyzed on the basis of normal-coordinate calculations of the planar s-cis form and a nonplanar gauche form. Such an analysis suggests that the second stable conformer takes a gauche form rather than the s-cis. To increase the number of reliable data to be used in this study, the infrared and Raman spectra of the d₀, 1,1,4,4-d ₄, and d₆ species were observed in low-temperature Ar matrices. The infrared spectra of the second stable conformer were also observed using a combination of the high-temperature nozzle and low-temperature matrix techniques.