High rotational excitation of molecular hydrogen in plasmas

Highly rotationally excited H2 molecules are observed in a hydrogen plasma. The rotational distribution, which is measured up to J = 17 in the vibrational state v = 2 is highly non-thermal. Whereas the lower rotational levels (J < 5) are distributed at the ambient temperature, the high rotational levels (J > 7) are distributed at a much higher temperature, close to the apparent vibrational temperature. The ro-vibrational distribution is compared to distributions observed in other plasma sources and all of the rotational distributions show strikingly similar non-thermal distributions. Of all the possible production mechanisms surface processes are strongly suggested to be responsible for the observed high rotational excitation.