EPR spectroscopy of the radical-molecular complex NH2-HF formed in low temperature chemical reaction of fluorine atoms with NH3 molecules trapped in solid argon

Chemical reactions of F atoms with NH3 molecules in a solid argon matrix we re studied with electron paramagnetic resonance (EPR) spectroscopy. Fluorin e atoms were generated by UV photolysis of F-2 molecules in dilute solution s of F-2 and NH3 in solid Ar. To distinguish reactions of photogenerated tr anslationally excited F atoms (at 15 K) from reactions of diffusing thermal F atoms (at T > 20 K) experiments were conducted at different temperatures . The radical-molecular complex NH2-HF is observed for the first time as an intermediate product in reactions involving both types of F atoms. The hyp erfine (hf) constants of the NH2-HF complex: a(N) = 1.20 mT, a(H) = 2.40 mT , and a(F) = 0.70 mT, were determined from analysis of EPR spectra in isoto pic substituted samples (N-14 --> N-15, and H --> D). The performed calcula tions revealed that complex NH2-HF has a planar C-2v structure and a bindin g energy of 12.3 kcal/mol. Optimisation of arrangement of the complex in an argon lattice shows that the complex suffers a minor distortion in crystal line lattice relative to its equilibrium geometry in a gas phase. Calculate d hf constants of the complex are in good agreement with those observed in EPR experiments. (C) 2000 Elsevier Science B.V. All rights reserved.