As a step toward licensing a lead–bismuth eutectic (LBE) based reactor design, the adsorption behavior of iodine evaporated from LBE on fused silica was examined. Using inert and reducing carrier gases, depositions with an adsorption enthalpy of − 95 to − 113 kJ mol ⁻¹ were observed. These depositions are compatible with a single species, tentatively identified as bismuth monoiodide, BiI. When introducing oxidizing conditions, multiple iodine species with higher volatility form, with adsorption enthalpies ranging from − 67 to − 86 kJ mol ⁻¹ . Based on an empirical correlation one of these species was identified as monatomic iodine. This work provides fundamental understanding of the LBE/iodine gaseous chemistry and related adsorption deposition behavior.