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.