Knowledge Bank

New electronic transitions of a carbon chain radical containing a nitrogen atom have been observed by LIF spectroscopy. The radical was produced in a supersonic jet by a pulsed discharge of $HC3N$ diluted to 0.3% with 3atm Ar. We confirmed that the radical contains a nitrogen atom from the fact that the spectrum was not observed when $C2H2$ was used as a precursor. About ten vibronic bands with a 50nsec radiative lifetime have been observed in a region from 27000 to $27400cm-1$. The observed bands could be classified as $\mathrm{<mrow\; data-mjx-texclass="ORD">2</mrow>}\Pi 3/2-2\Pi 3/2$ and $\mathrm{<mrow\; data-mjx-texclass="ORD">2</mrow>}\Sigma -2\Sigma$ vibronic bands. The lower state rotational constants of the vibronic bands have been determined to be 0.07537(1) and $0.07932(5)cm-1$ for the $\Pi$ and $\Sigma$ states, respectively. The upper states of $\mathrm{<mrow\; data-mjx-texclass="ORD">2</mrow>}\Sigma -2\Sigma$ bands have very large spin-rotation constants, which should be denoted as $\Sigma (\pm )$ subjected to a small Renner-Teller interaction. The new molecule has been tentatively assigned to be the $C4N$ radical. We performed an UMP2 level ab initio calculation with $6-311G\ast \ast$ basis sets for the $C4N$ radical. The estimated rotational constant in the ground state was $0.077cm-1$. This value agrees well with the observed rotational constants.