Gas temperature of molecular nitrogen (N-2) effusing out from a 40-mm-diameter 50-mm-long multicusp plasma source was measured by a mass separated time-of-flight (MSTOF) method. The measured signals of N-2 flux were fitted to a Maxwellian distribution to determine the gas temperature by the least squares method. The temperature of N-2 in the plasma was found to increase from 300 K to 410 K by striking a discharge with the power density of 3.3 W/cm(3). In accordance with the increase of the ion source discharge power, signals of atomic nitrogen flux increased while those of N-2 flux decreased corresponding to the dissociation of N-2 in the plasma source. (c) 2005 Published by Elsevier B.V.