In situ measurement of rovibrational populations of H2 ground electronic state in a plasma by VUV laser absorption

Hydrocarbon radicals interaction with amorphous carbon surfaces

“…This approach represents the true physical picture as there are no means in the PSI-2 experiments to suppress the rotationalvibrational excitations. It is also known that the total energy gained by the molecules in the plasma would have translational, rotational and vibrational contributions [19][20][21][22][23][24][25]. Spectroscopic measurements of the vibrational states have been in made in TEX-TOR [19].…”

New Developments with H− Sources

“…Development of early H-ion sources[ 171 were discussed in terms of single-step H-formation by electron bombardment of H2 [ 18,191. In the continuing development of pure H2 plasmas with a higher concentration of H 120,2 11 for sourcc applications, results were obtained which could not be explained in terms of cross sections discussed in [ 18,191. This work led to the suggestion that vibrationally excited H~( v ) molecules were fundamental to the enhanced H' production, which led to furlher experimenta1 [22,23] and theoretical [24] work confirming a two-step process in which cold electrons disassociate vibrationally excited H~( v ) molecules to Ji-and atomic hydrogen. This early work provided the basis for the two-chamber H-volume source where a driver region with high electron temperature is separated from the H-production region with a low electron temperature by a magnetic filter [25,26], A recent article [2'7] has summarized cross section data for electron-impact inelastic processes on vibrationally excited H2 molecules.…”

Relaxation behavior of rovibrationally excited H2 in a rarefied expansion

“…And this reaction becomes five orders of magnitude more efficient when the rovibrational energy of the hydrogen molecule is increased to around 2.5 eV. 21,22 Since in the plasmas used for the production of the H Ϫ ion, the high rotational levels are usually enormously overpopulated, 17,[23][24][25] these high rotational levels play an important role in the production of the negative hydrogen ion. Knowledge of the behavior of the high rotational levels is therefore required.…”

“…An advantage is the possibility of an absolute calibration. Alternative techniques to measure rotational and vibrational populations of molecular hydrogen are absorption spectroscopy 23,24 and laser induced fluorescence ͑LIF͒. 25,31 In the case of molecular hydrogen, the disadvantage of these techniques is that light in the vacuum-UV part of the spectrum has to be used.…”

“…The rovibrational population leaving the plasma source 30,31 shows a remarkable similarity with rovibrational distributions measured in other plasma environments. 17,[23][24][25] The higher rotational levels (Jу5) in all of the aforementioned studies are overpopulated, usually even by orders of magnitude. Although the measurements are performed in different experiments, under very different experimental conditions ͑pressure, temperature, electron density, and electron temperature͒ the distributions are stunningly similar.…”