A complete set of state-to-state rotational energy transfer rate constants has been measured for acetylene–acetylene collisions at room temperature under single collision conditions. Initial rotational states (Ji=5,7,...,25) were prepared and final states (Jf=1,...,25) interrogated. The measurements were carried out in a typical gas phase pump and probe arrangement. The initial vibrationally excited state was prepared by stimulated Raman pumping using strong Q-branch transitions. State preparation via this branch produces an isotropic spatial distribution of the excited state which is important for data analysis. Narrow bandwidth lasers ensure single rotational state selectivity. The rotational distribution after collisions is monitored by time-delayed laser-induced fluorescence via the Ã 1Au(ν3′ = 1)←X̃ 1Σg(ν2″ = 1) transition. In general, the rate constants decrease exponentially with the transferred rotational energy. The complete rate constant matrix can consistently be described by a simple parameter set within the dynamical infinite order sudden power approximation. In addition to this general behavior a significant ΔJ propensity of the rate constants is observed. Using the energy corrected sudden approximation with a power law basis an excellent match, reproducing the ΔJ propensities, to the rate constant matrix is obtained, again with a single set of parameters.

Articles you may be interested inInfluence of microwave driver coupling design on plasma density at Testbench for Ion sources Plasma Studies, a 2.45 GHz Electron Cyclotron Resonance Plasma Reactor Rev. Sci. Instrum. 85, 033310 (2014); 10.1063/1.4869343 Electron-temperature control in 915 MHz electron cyclotron resonance plasma Effect of discharge microwave frequency on electron temperature of electron cyclotron resonance plasma Rev. Sci. Instrum. 72, 1666 (2001); 10.1063/1.1347972 Multicomponent consideration of electron fraction of electron-cyclotron resonance source plasma Rev. Sci. Instrum. 71, 850 (2000)Electron cyclotron resonance ion source ionic currents (both in the stable and periodic regimes) modeled in relation with the hot electron temperature via the potential dip Rev.Spatial profiles of electron density and temperature of electron cyclotron resonance discharge plasmas have been successfully measured using laser Thomson scattering. The results, thus obtained, were valuable for quantitative comparison with results of a computer simulation. Measurements were performed for two cases with different locations of the electron cyclotron resonance zones. Simulation results obtained from a hybrid code, which treats ions and neutral particles as discrete particles and electrons as a fluid, were fitted to the experimental profiles of the electron density and temperature by adjusting the microwave power deposition profiles. From these comparisons and an analysis of other simulation data, it was found that the large difference of radial electron density profiles for two discharge conditions was caused by the difference of radial space-charge electric-field distributions. The radial electron temperature distribution determined the radial electric field that drove the ions radially and also resulted in a peaked electron density profile for one case and a more uniform profile for the other case. It is also shown that Coulomb collisions of electrons with ions as well as electron-neutral collisions are important for the analysis of electron behavior along the magnetic field lines.

The neutral atom density in an electron cyclotron resonance plasma has been directly measured for the first time using a combination of Rayleigh and Thomson scattering. The measurements were made in the source region of a 3 mTorr argon discharge, and indicated that the neutral atom density was at least 50% less than would be expected at a gas pressure of 3 mTorr. The decrease in the neutral atom density is attributed to the effect of ion-neutral charge exchange collisions in the plasma. The accuracy of the measurement was found to depend on the contribution of metastable atoms to the measured scattered signal.

Ion velocity distribution functions were measured using Doppler-shifted laser-induced fluorescence spectroscopy in an electron cyclotron resonance discharge in argon. The influence of the magnetic field configuration on the distributions was studied by making measurements with different magnetic field configurations. Results of a two-dimensional hybrid model of the discharge were used to help interpret the measured data. The results from the experiment and the simulation indicated that the magnetic field configuration had a strong influence on the ion velocity distribution functions. From the simulation it was concluded that the magnetic field configuration determined the axial distributions of plasma potential and electron density, and how these plasma parameters determined the ion velocity distribution function in the downstream region of the discharge.

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