A high‐energy pulsed electron beam has been used to dissociate fluorine molecules in fluorine, helium, CO2, and hydrogen chloride gaseous mixtures. By using a probe HF laser and monitoring the amount of ir absorption by hydrogen fluoride resulting from the rapid F + HCl → HF + Cl reaction in these mixtures, the fluorine atom concentration was determined. It was found that an upper limit of approximately three fluorine atoms is produced from each electron‐molecule ionizing collision.