15min:

P. VANKAN, S. B. S. HEIL, D. C. SCHRAM AND R. ENGELN, Department of Applied Physics, Centre for Plasma Physics and Radiation Technology (CPS), Eindhoven University of Technology, P.O. Box 513, NL-5600 MB Eindhoven, The Netherlands.

Rotationally and vibrationally excited hydrogen molecules are measured using Laser Induced Fluorescence (LIF) spectroscopy in the vacuum-UV. The laser radiation is generated via the Stimulated Anti-Stokes Raman Scattering (SARS) process, and is tunable between 120 nm and 230 nm. Up to 10 Anti-Stokes beams are simultaneously directed into the hydrogen plasma expansion. This so-called multiplex excitation makes an accurate wavelength calibration of the pump laser imperative. This calibration is performed by simultaneously recording the VUV-LIF signal from the plasma expansion and the well-known two-photon laser induced fluorescence spectrum of nitric oxide in a gas cell. The density of hydrogen molecules in the ro-vibrationally excited energy levels is calibrated on the basis of previously performed Coherent Anti-Stokes Raman Scattering measurements. Population distributions are measured in an expanding plasma to determine the production mechanism of the ro-vibrationally excited hydrogen molecules.

In this contribution we present results on the population distribution of H₂^r,v from v=2 to v=6 in the electronic ground state. The ro-vibrational population distribution in the expanding hydrogen plasma can be described with a two temperature Boltzmann distribution. The population distribution in the low rotational levels (J \leq 5) in the measured vibrational states can be described with a temperature of 800 K, while the higher rotational levels are populated according to a vibrational-like temperature of 3600 K. In the v=2 state rotational excitation is observed up to J=19. A possible generation mechanism for the super-rotational excitation is the association of atomic hydrogen at the reactor wall.