LIF SPECTROSCOPY OF A CARBON CHAIN RADICAL PRODUCED BY A $HC_{3}N$ DISCHARGE

Abstract

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 $HC_{3}N$ 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 $C_{2}H_{2}$ was used as a precursor. About ten vibronic bands with a 50nsec radiative lifetime have been observed in a region from 27000 to $27400 cm^{-1}$. The observed bands could be classified as $^{2}\Pi_{3/2}-^{2}\Pi_{3/2}$ and $^{2}\Sigma - ^{2}\Sigma$ 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 $^{2}\Sigma - ^{2}\Sigma$ 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 $C_{4}N$ radical. We performed an UMP2 level ab initio calculation with $6-311G^{\ast \ast}$ basis sets for the $C_{4}N$ radical. The estimated rotational constant in the ground state was $0.077 cm^{-1}$. This value agrees well with the observed rotational constants.