Vibrational kinetics in Cl$_{2}$ and O$_{2}$ low-pressure inductively-coupled plasmas

Low energy electron interactions with molecules via resonances can cause vibrational excitation (affecting chemical kinetics), electron energy loss and modification of the EEDF. However, with the exception of N$_{2}$ and H$_{2}$ plasmas, very little attention has been paid to this subject. We have implemented a novel high-sensitivity ultra-broadband UV absorption bench, allowing spectra to be recorded with noise as low as 2x10$^{-5}$ over a 250nm wavelength range, and recording of complete vibronic bands. We applied this to radiofrequency inductively-coupled plasmas in low pressure (5-50 mTorr) pure O$_{2}$ and pure Cl$_{2}$. In O$_{2}$ plasmas we surprisingly observe highly vibrationally excited O$_{2}$ (v'' up to 18) via B-X Schumann-Runge bands. Cl$_{2}$ molecules show a broad UV absorption spectrum in the region 250-400nm, with distinctly different absorption spectra for vibrationally excited molecules. However, only a small fraction of the Cl$_{2}$ molecules were observed in vibrationally excited states and the vibrational temperature is close to equilibrium with the local gas translational temperature (up to 1000K), in contrast to O$_{2}$. We are currently working on global models with vibrational kinetics to explain these results.