Small changes observed in the 19F isotropic hyperfine interaction in F2NO upon isotopic substitution of the N or O atom are shown to be statistically significant. The effect is attributed to a modulation of the hyperfine interaction by the ν2 bending mode of the free radical.
Endothermic Formation of a Chemical Bond by Entropic Stabilization: Difluoronitroxide Radical in Solid Argon
作者:Eugenii Ya. Misochko、Alexander V. Akimov、Ilya U. Goldschleger、Alexander I. Boldyrev、Charles A. Wight
DOI:10.1021/ja982222r
日期:1999.1.1
Difluoronitroxide radical (F2NO) has been formed in solid argon matrices by successive addition of two diffusing F atoms to NO. This radical exists in dynamic equilibrium with a van der Waals complex (F-FNO). Measurements of the equilibrium concentrations as a function of temperature show that the changes in enthalpy and the entropy associated with formation of the F2NO radical are Delta H = 1240 +/- 180 J/mol and Delta S = 62 +/- 10 J/(mol K). Because both these quantities are positive, the equilibrium favors F2NO only at elevated temperatures. This situation is a rare case in which formation of a chemical bond is stabilized only by an increase in the entropy of the system.