Infrared and EPR spectroscopic study of open-shell reactive intermediates:F+NH3 in solid argon

Mobile F atoms react with NH3 molecules in an argon matrix at temperatures T=7-35 K. The open-shell NH2-HF complex was observed by EPR and infrared sp ectroscopies as the main product of this reaction. The hyperfine constants of the NH2-HF complex a(N)=1.20 mT, a(H)=2.40 mT, and a(F)=0.70 mT were det ermined from the EPR spectra of samples using NH3, (NH3)-N-15 and ND3 isoto pomers. Prominent features of the infrared spectrum of NH2-HF are a strongl y red-shifted HF stretching mode (Deltav approximate to -720 cm(-1) relativ e to that for isolated HF) and strong absorptions at 791 and 798 cm(-1) att ributed to HF librational modes in the complex. Quantum chemistry calculati ons reveal that the hydrogen-bonded NH2-HF complex has a planar C-2v struct ure and a binding energy of 51 kJ/mol. Calculated hyperfine constants and v ibrational frequencies of the complex are in good agreement with those obse rved in the EPR and IR experiments. (C) 2000 American Institute of Physics. [S1063-777X(00)01409-2].