Knowledge Bank

We have observed about 700 lines of the absorption spectrum of molecular hydrogen arising from transitions between the $2c3\Pi u$ state and the $n=3\Sigma \Pi V$ complex using the technique of dye laser intracavity absorption. Because of the nature of the energy levels one component of the $\lambda$ doublet of each rotational level of the 2c state predissociates with a lifetime of the order of $2\times 10-9$ sec, while the non-predissociative component has a lifetime of about $8\times 10-5$ sec, for radiative decay. This would suggest that the density of molecules in the predissociative states should be at least a factor of $10-5$ smaller than that of the non-predissciative state. Our data shows that in an rf produced hydrogen plasma the intensities of the two kinds of transitions are comparable. The linearity of our ICA system has been demonstrated by measuring the quenching rate of the $2c,v=2,N=1$ state by Ne, and obtaining the same result given by Tischer and Phelps1. Our data suggests that there is a mechanism operating in the plasma which preferentially populates the predissociative states, and some suggestions as to its nature will be presented.