Knowledge Bank

Butadiene-trans,trans-1,$4-d2$ and -cis,cis-1,$4-d2$ were prepared from trans,trans-1,4-dichlorobutadiene. Gas-phase spectra were recorded at $0.002cm-1$ resolution in the mid-infrared region on a Bruker IFS 120HR FT spectrometer at PNNL. For the trans,trans isotopomer the C-type band at $1002.553cm-1$ which was not perturbed near the band center, was more fully analyzed than another C-type band at $825.5cm-1$, which was extensively perturbed. Ground state rotational constants for this near-symmetric top $(\kappa =-0.9810)$ were fit to 1828 ground state combination differences (GSCDs) derived from the two bands. A, B and C rotational constants for the ground state are 1.3397796(7), 0.1306985(2), and $0.1191086(3)cm-1$ respectively. For the cis,cis isotopomer the C-type band at $808.367cm-1$ was analyzed. Fitting 1559 GSCDs gave $\kappa =-0.9707$ and 1.1398737(6), 0.1380156(3), and $0.1231302(3)cm-1$ for A, B and C, respectively. These rotational constants along with those of other deuterium and $\mathrm{<mrow\; data-mjx-texclass="ORD">13</mrow>}C$ isotopomers will be used to determine a complete equilibrium rotational structure of butadiene.