The trihalogens IIF and ClIF and the pseudo-trihalogen HIF have been directly observed as the products of the endoergic bimolecular reactions of F₂ with I₂, ICl and HI in a crossed molecular beam experiment. At high collision energies a second reactive channel producing IF becomes important. Product angular and velocity distributions show that this IF does not result from a four-centre exchange reaction. Observed threshold energies for the formation of IIF, ClIF and HIF yield lower bounds on the stability of these molecules (with respect to the separated atoms of 69, 81 and 96 kcal mol^–1, respectively). Analysis of the product centre-of-mass angular distributions indicate that a slightly non-linear approach is most effective in bringing about reaction to form the stable triatomic radical. These studies reveal a potentially important mechanism for the F₂+ I₂→ 2IF bulk gas phase reaction.