Inductively-coupled plasmas in molecular, electronegative gases are widely used for plasma processing of surfaces, for instance in CMOS manufacture. The complexity of these systems is such that they can only be described by multi-physics models which describe both the plasma physics and the molecular collisional processes. However, rigorous validation of these models by comparison to quantitative measurements of particle densities over a wide range of parameter space has not been performed. We have chosen to study the Cl2/O2 system because of the industrial process relevance but also because methods exist to measure the density of many of the particles present. Electron densities were measured by microwave hairpin resonator. Absolute Cl and O atom densities were determined by Two-photon Absorption Laser-Induced Fluorescence [1, 2]. A new ultra-low noise broadband UV-visible absorption bench [3] allows measurement of the densities of ground state Cl2 molecules, ClxOy reaction products and vibrationally excited states of Cl2 and O2. Whereas plasmas in O2 show high vibrational excitation (up to 10,000K) with gas translational temperatures reaching up to 900K, in Cl2 the vibrational temperature is in equilibrium with the gas translational temperature (about 1000K). These results will be compared to the current state of the art in 2-D hybrid fluid models as well as simpler global models, allowing the chemical and energy transfer mechanisms to be understood. 1) Booth, J.P., Y. Azamoum, N. Sirse, and P. Chabert, Journal of Physics D: Applied Physics, 45, 195201. (2012) 2) Niemi, K., V. Schulz-von der Gathen, and H.F. Dobele, Plasma Sources Science & Technology, 14, (2005) 3) Foucher, M., D. Marinov, E. Carbone, P. Chabert, and J.-P. Booth, Plasma Sources Science and Technology, 24, (2015)