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

Abstract

Photoinduced reactions in binary NH 3 -F 2 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 [H 2 N • -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 FH 2 N-HF and NH-HF-HF complexes in approximately equal amounts. Isotopic substitution experiments using 15 NH 3 and ND 3 aided the assignments of the infrared bands of NH-HF-HF, which is identified for the first time. Thermal recombination of the [H 2 N • -HF‚‚‚F • ] radical pairs at 20 K yields only the addition product FH 2 N-HF. However, photoinduced recombination of [H 2 N • -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 e 355 nm.

Mercury–fluorine interactions: a matrix isolation investigation of Hg⋯F2, HgF2 and HgF4 in argon matrices

“…In the case of previous F 2 matrix photochemistry it has been shown that in the case of the Group 15 hydrides, NH 3 forms a F 2 -NH 3 complex with n FÀF at 781 cm À1 on deposition, which is readily photoconverted to FH 2 N-HF. 70 More recent work has shown that the initial photoproduct is [H 2 N -HFÁ Á ÁF ] which converts to FH 2 N-HF on annealing to 19 K. 71 This work has also shown that the formation of [H 2 N -HFÁ Á ÁF ] is twenty times greater than the expected rate of F 2 photodissociation. F 2 and N 2 H 4 form N 2 H 3 F-HF spontaneously on deposition.…”

Trapping and thermal migration of the first- and second-row atoms in Ar, Kr and Xe crystals

“…The TIM activation threshold in Kr was determined to be 15 K, 42 in sharp contrast to all other interstitial atoms which are more readily activated in Ar. Akimov et al 41 reported the TIM diffusion coefficient in Ar at 25 K, 3 Â 10 À15 cm 2 s À1 , which corresponds to k = 13 s À1 . Our isotropic result is 20 s À1 .…”

“…Direct and indirect indications of the TIM were reported for the majority of the first-and second-row atoms, namely, for H, [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19] Li, 20,21 B, 22,23 C, [24][25][26][27][28][29] N, [30][31][32][33][34] O (see ref. 35 and references therein) and F. [36][37][38][39][40][41][42] However, the TIM activation energies and rates were reliably determined in the selected RG matrices only for H [5][6][7]9,12,13,15 and O 31,…”

Modern applications of matrix isolation technique to investigation of radical species generated in atom–molecular chemical reactions

“…At the same time, the reaction channels (6a) and (6b) can be significant for the complexes with HI (HBr) or F 2 molecules due to weakening of the cage effect for the hydrogen and fluorine atoms compared to the heavy halogen atoms. 60 Photolysis of isolated molecules in cryogenic matrices is a conventional method of generation of stabilised radicals. Spectro-hn hn scopic data for the radical species thus produced served as the basis for further studies of these objects (see, e.g., Ref.…”