Observation of the I′ 1Πg outer well state in H2 and D2

Abstract

We observed bound levels of the I′ state in H2 and D2, confined in the outer well of the lowest Πg1 adiabatic potential close to its (1s+2p) dissociation limit, with an equilibrium internuclear distance of ≈8 a.u. Rovibronic levels (v=0–2, J=1–5 for H2 and v=0–5, J=1–6 for D2) are populated with pulsed lasers in resonance enhanced XUV+IR (extreme ultraviolet+infrared) excitation, and probed by a third laser pulse. Level energies are measured with an accuracy of ≈0.03 cm−1, and are in reasonable agreement with predictions from ab initio calculations in adiabatic approximation; the smallness of Λ-doublet splitting indicating that nonadiabatic interactions with Σg+1 states are generally weak. Additional resonances are observed close to the n=2 dissociation limit, some of which can be assigned as high vibrational levels of the EF 1Σg+ state.