Precision measurement of quasi-bound resonances in H${}_2$ and the H + H scattering length

Abstract

Quasi-bound resonances of H${}_2$ are produced via two-photon photolysis of H${}_2$S molecules as reactive intermediates or transition states, and detected before decay of the parent molecule into three separate atoms. As was previously reported [K.F. Lai et al., Phys. Rev. Lett. 127, 183001 (2021)] four centrifugally bound quantum resonances with lifetimes of multiple $\mu$s, lying energetically above the dissociation limit of the electronic ground state X${}^1{\Sigma }_g^{+}$ of H${}_2$, were observed as X($v,J$) = (7,21)${}^{\ast }$, (8,19)${}^{\ast }$, (9,17)${}^{\ast }$, and (10,15)${}^{\ast }$, while also the short-lived ($\sim 1.5$ ns) quasi-bound resonance X(11,13)${}^{\ast }$ was probed. The present paper gives a detailed account on the identification of the quasi-bound or shape resonances, based on laser detection via F-X two-photon transitions, and their strongly enhanced Franck-Condon factors due to the shifting of the wave function density to large internuclear separation. In addition, the assignment of the rotational quantum number is verified by subsequent multi-step laser excitation into autoionization continuum resonances. Existing frameworks of full-fledged ab initio computations for the bound region in H${}_2$, including Born-Oppenheimer, adiabatic, non-adiabatic, relativistic and quantum-electrodynamic contributions, are extended into the energetic range above the dissociation energy. These comprehensive calculations are compared to the accurate measurements of energies of quasi-bound resonances, finding excellent agreement. Etc.

Accepted Molecular Physics

References in corpus (9)

• Benchmarking theory with an improved measurement of the ionization and dissociation energies of H${}_2$
• Constraints on extra dimensions from precision molecular spectroscopy
• Observation and calculation of the quasi-bound rovibrational levels of the electronic ground state of H${}_2^{+}$
• Precision measurement of the fundamental vibrational frequencies of tritium-bearing hydrogen molecules: T${}_2$, DT, HT
• Precision spectroscopy of high rotational states in H_2 investigated by Doppler-free two-photon laser spectroscopy in the EF^1Σ_g^+ - X^1Σ_g^+ system
• Accurate Born-Oppenheimer potentials for excited ${\Sigma }^{+}$ states of the hydrogen molecule
• Photolysis production and spectroscopic investigation of the highest vibrational states in H${}_2$ (X${}^1{\Sigma }_g^{+}$ $v=13,14$)
• Shape resonances in H${}_2$ as photolysis reaction intermediates
• Two-photon Doppler-free ultraviolet laser spectroscopy on sulphur atoms

Cited by in corpus (1)

• Spectroscopic study of the F${}^1{\Sigma }_g^{+}$ outer well state in H${}_2$, HD and D${}_2$