HIGH RESOLUTION FAR INFRARED FOURIER TRANSFORM SPECTROSCOPY OF THE NH$_2$ RADICAL.

Abstract

Author Institution: SOLEIL Synchrotron, AILES beamline, Saint-Aubin, France and Institut des Sciences Moleculaires d'Orsay, ISMO, CNRS, Universite Paris XI, Orsay, France; SOLEIL Synchrotron, AILES beamline, Saint-Aubin, FranceFirst identified toward Sgr B2}, the NH$_2$ radical has recently been detected in the interstellar medium by the HIFI instrument on board of Herschel}. Despite the fact that this radical has not been detected in brown dwarfs and exoplanets yet, it is already included in physical and chemical models of those environments} (temperature higher than 2000 K expected in several objects). Its detection in those objects will depend on the existence of a reliable high temperature and high resolution spectroscopic database on the NH$_2$ radical.The absorption spectrum of NH$_2$ has been recorded between 15 and 700 cm$^{-1}$ at the highest resolution available using the Bruker IFS125HR Fourier transform interferometer connected to the far infrared AILES beamline at SOLEIL (R=0.001~cm$^{-1}$). The radical was produced by an electrical discharge (DC) through a continuous flow of NH$_3$ and He using the White-type discharge cell developped on the beamline (optical path: 24m). Thanks to the brilliance of the synchrotron radiation, more than 700 pure rotational transitions of NH$_2$ have been identified with high N values (N$_{max}$=25) in its fundamental and first excited vibrational modes. By comparison to the previous FT spectroscopic study on that radical in the FIR spectral range}, asymmetric splitting as well as fine and hyperfine structure have been resolved for several transitions