ABSOLUTE RATES OF RECOMBINATION AND DISPROPORTIONATION OF DIMETHYLAMINYL RADICALS

The absolute rate constants for the recombination (k(r)) and disproportionation (k(d)) reactions of dimethylaminyl radicals were determined at room temperature with the very low pressure reactor (VLPR) technique. The obtained values were k(r) = (1.70 +/- 0.19) X 10(-12) cm3 molecule-1 s-1 and k(d) = (4.19 +/- 0.52) x 10(-12) cm3 molecule-1 s-1, and the ratio k(d)/k(r) was 2.32 +/- 0.26. The transition-state geometries for both recombination and disproportionation reactions are loose, with the N...N bond length ca. 3.5 angstrom and the N...H...C distance ca. 4.4 angstrom. In the recombination TS, the four C-N...N bending modes are ca. 90 cm-1 and play a significant role in the formation of the N-N bond in tetramethylhydrazine. In the disproportionation TS, the two (in-plane and out-of-plane) vibrational modes of the metathetic hydrogen are ca. 110 cm-1 and are essential in the formation of the N-H bond in dimethylamine.