Rotational and vibrational state distribution of H_2 activated on a heated tungsten filament

The rotational and vibrational state distributions of H_2 activated on a heated tungsten filament were determined by employing a coherent anti-Stokes Raman scattering technique to examine the contribution to the catalytic chemical vapor deposition process. The rotational excitation could be confirmed and the distribution was Boltzmann-like. When the filament temperature was 2700 K and the H_2 pressure was over 1.3 kPa, the rotational temperature monitored 5 cm under the filament was around 1200 K; it showed a sharp decrease below 670 Pa and it was 700 K at 67 Pa. This decrease in the rotational temperature suggests the importance of relaxation processes on the chamber walls. The first vibrationally excited H_2 molecules could also be identified at pressures over 670 Pa and the vibrational temperature was not much different from the rotational one. This vibrational temperature is much lower than those in typical H_2 plasma, showing that the direct vibrational excitation of H_2 on hot filaments is inefficient compared to its dissociation to two H atoms