Abstract The surface lifetimes of fluorine, chlorine, bromine and iodine adsorbed on a molybdenum surface have been obtained from measurements of the halide ion desorption flux using the modulated molecular beam technique. Measurements were made at temperatures between 1350 and 1850 K and at surface coverages of less than 10 10 halogen atoms cm −2. The temperature-lifetime data were fitted to an Arrhenius expression from which the binding energies l̄, and pre-exponential factors τ̄ 0, were obtained: F: l ̄ = 4.65 eV and τ ̄ 0 = 3 × 10 −16 s ; Cl: l ̄ = 4.11 eV and τ ̄ 0 = 3 × 10 −16 s ; Br: l ̄ = 3.70 eV and τ ̄ 0 = 2 × 10 −15 s ; I: l ̄ = 3.15 eV and τ ̄ 0 = 1 × 10 −16 s . It was concluded that the halogens are adsorbed as strongly bound surface compounds, MoX (where X is either F, Cl, Br, or I) from which gaseous ions and neutral atoms desorb at rates consistent with the Saha-Langmuir relationship. From that relationship and the above data, separate binding energies and pre-exponentials were calculated for ion and neutral desorption. The importance of the desorption of MoX was assessed.