Chlorine atom densities in the (3p<SUP>5</SUP>)<SUP>2</SUP> P<SUP>0</SUP><SUB>1/2</SUB> excited spin-orbit state measured by two-photon absorption laser-induced fluorescence in a chlorine inductively coupled plasma

International audienceChlorine atom densities in the spinorbit excited state were measured by two-photon absorption laser-induced fluorescence (TALIF) in an inductively coupled plasma discharge in pure Cl2. The atoms were excited by two photons at 235.702 nm to the state and detected by fluorescence to the (4s) 4P5/2 state at 726 nm. The population of this state relative to that in the ground state, was determined from the relative TALIF signal intensity from the two states, combined with new calculations of the two-photon absorption cross-sections. was found to increase continuously with radio-frequency power (50500 W), whereas with Cl2 pressure (590 mTorr) it passes through a maximum at 10 mTorr, reaching ~30% at 500 W. This maximum corresponds to the maximum of electron density in the discharge. Combining this density ratio measurement with previous measurements of the absolute ground state chlorine atom density [1] allows the absolute spin-orbit excited state density to be estimated. A significant fraction of the total chlorine atom density is in this excited state which should be included in plasma chemistry models