Re-investigation of the infrared spectrum of the NCN radical by laser magnetic resonance spectroscopy

Abstract

The laser magnetic resonance (LMR) spectroscopic technique has been used to reinvestigate the mid-infrared spectrum of the NCN free radical in its Σg-3 ground electronic state. A liquid nitrogen-cooled carbon monoxide (CO) laser was used as a source of strong coherent radiation in the 1442–1484 cm−1 region of the infrared. Vibration-rotation transitions were brought into resonance with the laser frequency using magnetic flux densities up to 1.4 T. Spectra were recorded in both parallel (ΔMJ = 0) and perpendicular (ΔMJ = ±1) polarizations with ten CO laser lines. Over one hundred new absorption lines were observed in the LMR spectra and have been subsequently assigned to transitions in either the 301 fundamental band (near 1466.5 cm−1) or the 211301 hot band (near 1455.6 cm−1) of NCN in the Σg-3 ground state. An improved set of molecular parameters for NCN has been determined from a least-squares fit of all the available data on the infrared spectrum, provided by Fourier transform and LMR spectra. In the wake of an exhaustive analysis of the LMR spectra, several additional lines remain. Although chemical tests indicate these lines do not belong to NCN, it has not proved possible to identify their carrier(s).