Photochemical Formation and Reaction of Radical Pairs from NH3−F2 Complexes Isolated in Solid Argon

Abstract

Photoinduced reactions in binary NH3−F2 complexes in solid argon are studied by FTIR spectroscopy. Analysis of the IR spectra and kinetics of product formation shows that the main photochemical channel at 355 nm is the formation of [H2N•−HF···F•] radical pairs; the relative initial yield of this product is 0.55. We believe that this is the first observation of this mechanism of radical pair formation (i.e., by escape of one of the F atoms from the initial cage containing the complex). The other major product channels form FH2N−HF and NH−HF−HF complexes in approximately equal amounts. Isotopic substitution experiments using 15NH3 and ND3 aided the assignments of the infrared bands of NH−HF−HF, which is identified for the first time. Thermal recombination of the [H2N•−HF···F•] radical pairs at 20 K yields only the addition product FH2N−HF. However, photoinduced recombination of [H2N•−HF···F•] radical pairs at 633, 532, 355, and 266 nm gives predominantly NH−HF−HF complexes. The relative yield of this secondary photolysis product increases with increasing energy of photoexcitation and is close to unity at λ ≤ 355 nm.