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

Low-Temperature Physics and Chemistry in Cryomatrice

Анотація

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 spectroscopies 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 determined from the EPR spectra of samples using NH₃, ¹⁵NH₃ and ND₃ isotopomers. Prominent features of the infrared spectrum of NH₂√HF are a strongly red-shifted HF stretching mode (Dn≈ - 720 cm^-1 relative to that for isolated HF) and strong absorptions at 791 and 798 cm^-1 attributed to HF librational modes in the complex. Quantum chemistry calculations reveal that the hydrogen-bonded NH₂ √HF complex has a planar C_2n structure and a binding energy of 51 kJ/mol. Calculated hyperfine constants and vibrational frequencies of the complex are in good agreement with those observed in the EPR and IR experiments.