Spatially resolved neutral gas temperature of Ar plasmas within a new type of transformer-coupled toroidal plasma source was measured by fitting unresolved rovibrational bands of trace gas N-2 (C (3)Pi(u) --> B (3)Pi(g)). With power density as high as 4.8 W/cm(3), the maximum neutral gas temperature inside Ar plasmas was found to be 2000 K. The position with maximum neutral gas temperature was off the center of the cross section and close to the ferrite core, where higher electric field contributes to higher heating power. The dependence of neutral gas temperature on pressure was measured and can be empirically fitted by proportionality between gas temperature and logarithm of the pressure, as found by other researchers. A simple physical model gives the dependence of pressure as the sixth order of neutral gas temperature, which fits the experimental data as well. It was also found that added N-2 gas perturbed Ar plasmas obviously, and therefore we recommend adding less than 1% N-2 as trace gas. There is no dependence of fitted neutral gas temperature on the optical resolution of monochromator, as would be expected. (C) 2004 The American Vacuum Society.