Experimental and theoretical studies of excited states of H2 observed in the absorption spectrum: I. The 5pπD″ 1Πu state

Abstract

The 5pπD″−X absorption lines of H2 have been reinvestigated using synchrotron radiation with a resolution of 0.001nm, in an experiment that also yields the absolute absorption intensity for each observed transition. New assignments have been made which extend the manifold of known levels up to the H(n=4)+H(1s) dissociation threshold. The observations are interpreted in the framework of Multichannel Quantum Defect Theory (MQDT), implemented here in a pure first principles approach based on the best available quantum chemical clamped-nuclei potential energy curves of Wolniewicz and collaborators [1,2]. The approach provides theoretical values for the transition energies, intensities, natural widths and quantum yields. Very good agreement is found in general between experiment and theory (to within ≈1–2cm−1 for the transition energies). An exception concerns the 5pπ, v=2, N=2 positive total parity state for which the ionization width is calculated by 40% too large.