Photoionization and photodissociation dynamics of H2 after (3+1) resonance-enhanced multiphoton ionization via the B 1Σu+ state

Abstract

We present a study of the molecular photoionization and photodissociation processes in molecular hydrogen occurring after one-photon absorption from various rovibrational levels (v′=3–22, J′=0–3) of the B 1Σu+(1sσg)(2pσu) state using resonance-enhanced multiphoton ionization in combination with high-resolution photoelectron spectroscopy (REMPI-PES). For one-photon absorption from the v′=3–8 levels, molecular photoionization competes with photodissociation into a ground-state atom and an atom in an n=2 excited state. A detailed comparison of the photoelectron spectra obtained via different rotational branches and vibrational levels strongly indicates that singly excited bound Σg+1 and Πg1 Rydberg states at the four-photon level exert a significant influence on the final state distributions of H2+. In contrast, one-photon absorption from the v′=9 and higher levels leads almost exclusively to dissociation into a ground-state atom and an excited-state atom with n>2. Excited atomic fragments are ionized in a one-photon absorption step, and excited-atom distributions over the energetically allowed values of the principal quantum number n are obtained. Simulations of these distributions suggest that excitation of dissociative continua of bound Σg+1(1sσg)(nsσg), Σg+1(1sσg)(ndσg), and Πg1(1sσg)(ndπg) Rydberg states may dominate over excitation of dissociative doubly excited Σg+1(2pσu)(npσu) and Πg1(2pσu)(npπu) states when considering the dissociation dynamics after one-photon absorption from the v′⩾9 levels of the B-state.