THE THERMAL-DECOMPOSITION OF NH2 AND NH RADICALS

The formation of NH2 and NN radicals as well as H and N atoms during t he thermal decomposition of hydrazine was investigated over a wide tem perature range. For the first time frequency-modulated spectroscopy wa s used for the detection of NH2 radicals behind shock waves. In compar ison with the dual beam laser absorption technique, the detection Zi;n it has been improved by one and a half orders of magnitude. For reacti on (5a) NH2+M-->NH+H+M the rare constants were obtained in the tempera ture range from 2200 to 4000 IC k(5a)=(1.2+/-0.5)10(15). exp [-(318+/- 10) kJ mol(-1)/RT] cm(3)/mol s and for reaction (6) NH+M --> N+H+M in the temperature range from 2500 to 3400 K k(6)=(1.8+/-0.8)10(14). exp [-(313+/-15) kJ mol(-1)/RT] cm(3)/mol s. The experimental apparent act ivation energies were found to be in good agreement with theoretical c alculations and recently recommended enthalpies of formation for NH2 a nd NH. The competing NH2 decomposition channel (5b) NH2+M-->N+H-2+M wa s shown to be of minor importance (less than or equal to 5%). The kine tic behavior of the unimolecular decomposition of NH is compared with that of H2O and (CH2)-C-3.