Photodissociation into H(1S)+H(n=2) atoms: Total and partial dissociation cross sections and relative importance of dissociation and predissociation

The total cross section for the photodissociation of H₂ into H(1S)+H(n=2) between 85.0 and 77.0 nm has been measured using synchrotron radiation at high resolution (0.005-nm bandwidth). This continuum is made up of three contributions from B, B' ¹{{Σ}}ᵤ⁺$, and C ${}¹Πᵤ. The B' photodissociation cross section is obtained directly at some excitation wavelengths from analysis of predissociation Fano profiles. The data are compared to computed values. The contribution of predissociated levels to the production of H(n=2)+H(1S) atoms for white-light excitation is found to be more than two times more efficient than the direct photodissociation.