H2 and D2 photon impact predissociation

Atomic Lyman α and Balmer α, β, and γ emission have been observed by irradiating H2 and D2 in the 680–860 Å region with synchrotron radiation from the ACO storage ring at Orsay. Comparison of the observed excitation spectra with the absorption spectrum shows clear evidence for the predissociation of molecular Rydberg states above the dissociation thresholds which are observed for the dissociation reactions: H2+hν→H(1S) +H* (n=2, 3, 4, 5). Undispersed visible fluorescence is also observed on excitation in the 750–860 Å region which is attributed to molecular emission from excited Rydberg states. The results of these photon impact experiments are compared with those from electron impact processes.