Reactions of photogenerated fluorine atoms with molecules trapped in solid argon 3.~* Formation of stabilized .NH_2 radicals and .NH_2-HF radical-molecule complexes in the reactions of fluorine atoms with NH_3 molecules

摘要

Isolated radicals .NH_2 and radical-molecule complexes .NH_2-HF, which are products of the reactions of mobile fluorine atoms with NH_3 molecules in solid argon, were identirird by EPR specrtoscopy. The isotropic HFC dconstants of the complex (a_N = 1.20, a_h = 2.40, and a_F = 0.70 mT) were determined experimentally. The cons6tant of isotropic HFC with the nucleus of hydrogen atom of the HF molecule is less than 0.1mT. This assignment was confirmed in the experiments on isotope substitutiojn of atoms (H->D, ~(14)N->~(15)N) in the NH_3 molecule. According to quantum-chemical calculations, the free comples NH_2-HF has a planar structure with C_(2v) symmetry and a binding energy of 12 kcal mol~(-1). Optimization of the arrangement of the complex in the crystal showed that its structure is only slightly distorted in the Ar lattice so that the equilibrium configuration is close to that obtained from gas-phase calculations. Different ratios of relative intensities of the proton triplet lines in the EPR spectra of isolated .NH_2 radicals ans .NH_2-HF complexes were qualittively explained by different heights of the barriers to rotation of the NH_2 fragment in the Ar Lattice