Time resolved spectroscopy and electron concentration measurements were performed on an Ar–He–F2mixture excited by an external rf antenna creating a plasma with features of a plasma source generated by a Helicon reactor commonly used in materials processing. The low pressure range and the simplified chemistry allow an appropriate modelling of some processes and lead to the determination of some fundamental data concerning atomic and molecular fluorine. We give a F2direct dissociation coefficient by electron impact of about 2.0×10−9cm3 s−1for an electron temperature of 5 eV. Excitation rate coefficients of some fluorine levels (3p 2P3/2, 3p 4D7/2, and 3p′ 2F7/2) are given as well as rate coefficients of line emissions following F2dissociation by electron impact. ©1995 American Institute of Physics.