Knowledge Bank

The N = 1 - 0 microwave transitions of the ground $\mathrm{<mrow\; data-mjx-texclass="ORD">2</mrow>}\Sigma +$ electronic state of all four singly substituted $\mathrm{<mrow\; data-mjx-texclass="ORD">13</mrow>}C$ isotopomers of linear CCCCH have been measured by pulsed-jet Fourier transform microwave spectoscopy. The 1-0 rotational transition is split into many resolvable components due to hyperfine interactions between the electronic spin and a) the molecular rotation, b) the spin of the proton, and c) the nuclear spin of the $\mathrm{<mrow\; data-mjx-texclass="ORD">13</mrow>}C$. The microwave transition frequencies are combined with the millimeter-wave $data1$ to produce a consistent set of rotational and hyperfine interaction constants. In particular, the Fermi contact interaction of the $\mathrm{<mrow\; data-mjx-texclass="ORD">13</mrow>}C$ nucleus has been measured for each of the substituted positions to provide information on the unpaired spin density along the carbon chain. The Fermi contact constants, $bF(13C)$, of 396.8(6),57.49(5),-9.54(2), and 18.56(4) MHz, for successive $\mathrm{<mrow\; data-mjx-texclass="ORD">13</mrow>}C$ substitutions starting furthest from the hydrogen are consistent with an electronic structure which is represented as mainly. $C\equiv C-C\equiv C-H$.