Matrix-Isolation Infrared Spectrum of the Free Radical NH2

Abstract

The free radical NH2 has been produced in concentration sufficient for direct infrared detection by photolysis of ammonia isolated in argon, nitrogen, and carbon monoxide matrices at 14°K with microwave-powered hydrogen and xenon discharges. Ultraviolet absorptions characteristic of both NH and NH2 are observed in photolyzed argon and nitrogen matrix samples. In the CO matrix, infrared observations show a high concentration of HCO after photolysis, further demonstrating the production of H atoms by the photolysis of ammonia. Two of the infrared fundamentals of 14NH2, at 1499 and 3220 cm−1, and of 15NH2, at 1495.5 and 3215 cm−1, one of NHD, at 1321 cm−1, and one of ND2, at 1110 cm−1, have been observed. Spectra observed in an argon matrix are relatively complex, suggesting that rotation of NH2 may be possible in this matrix. The force constants and thermodynamic properties of NH2 are estimated. The photolysis of matrix-isolated ammonia has been found to be relatively inefficient, in contrast to an earlier prediction.