Knowledge Bank

The $\mu a$ spectra of the eight monosubstituted isotopic species of trans-acrolein have been obtained, and the complete $r4$ structure has been determined. Two doubly substituted species and three triply substituted species were studied to make certain that the nearly equivalent positions of two carbon atoms and two hydrogen atoms were correctly identified. The bond lengths are $ra(C=O)=1.220\backslash AA,ra(CH)ald.=1.105\backslash AA,ra(C-C)=1.472\backslash AA,ra(CH)=1.079\backslash AA,ra(C=C)=1.344\backslash AA$, and $ra(CH)=1.086\backslash AA$ for both bonds of the $CH2$ group. The bond angles are $\sphericalangle CCO=123.0\circ ,\sphericalangle CCH(ald.)=115.3\circ ,\sphericalangle CCH(vinyl)=118.0\circ ,\sphericalangle CCC=119.7\circ$, and $\sphericalangle HCH=118.5\circ$ with the $CH2$ group titled $0.7\circ$ toward the aldehyde H atom. The $\mu b$ spectra were observed for the ground state and $v=1$ torsional state of the normal species. The inertial defects were found to be negative, $\Delta =-0.021$ amu$\backslash AA2$ for the ground state, and $\Delta =-0.223$ for the $v=1$ torsional state.