Production and loss of rovibrationally excited H2 molecules: Expanding hydrogen plasmas in experiment and model

摘要

The rovibrationally resolved density distributions of molecular hydrogen are measured inexpanding thermal hydrogen plasmas by means of laser induced fluorescence in the vacuum-UVrange (VUV-LIF). The results reveal a non-Boltzmann distributions, where the low rotational states(J = 1-6) follow a temperature of 700 K, while the higher rotational states are overpopulatedcompared to these lower states and follow higher temperatures up to 4500 K. Experiments wereperformed under variation of the surface area in the plasma source by varying the nozzle length.We assume surface association processes of atomic hydrogen at the surface of the nozzle,producing rovibrationally excited H2 molecules. While the atomic hydrogen flow decreases withincreasing surface areas, the H2rv distribution shows a more pronounced non-Boltzmann behaviour.A simple 0D model of (de)excitation processes by collisions with electrons and neutrals results inadditional information about the formation of the measured H2rv distributions.