[Full text not available yet]This paper deals with optical emission spectroscopy studies of low pressure (0.1–0.5 Torr) capacitively coupled radiofrequency hydrocarbon/argon-rich plasmas used for the synthesis of nanocarbon structures. The main goal of this paper is to obtain the electron temperature of such far-from-equilibrium plasmas as a function of the pressure, the excitation power and the argon content. In doing so, we have found that the argon upper energy levels used for electron temperature estimation remain close to corona balance. The latter has allowed us to use a modified Boltzmann plot technique to derive the electron temperature. It was found that, for the plasmas investigated, an increase of the argon population density (from 10% to 95%) leads to a pronounced decrease of the electron temperature while an increase of the processing pressure produces a moderate increase of the electron temperature. Additionally, the increase of the power from 50 to 300W produces a very slight growth of the electron temperature.This work has been partially financed by the Spanish National Project (MAT2002-04085-C02-02). One of the authors (MC) is indebted to CSIC (Consejo Superior de Investigaciones Científicas) for financial help.Peer reviewed