Shape resonances in H$_2$ as photolysis reaction intermediates

TL;DR

This study measures shape resonances in H$_2$ molecules formed during photolysis of H$_2$S, confirming theoretical predictions and observing nonadiabatic and QED effects in neutral atom collisions for the first time.

Contribution

First experimental observation of nonadiabatic and quantum electrodynamical effects in shape resonances of neutral atom collisions, with high-precision measurements matching advanced theoretical models.

Findings

Resonance lifetimes range from nanoseconds to milliseconds.

Resonance positions agree with theory including nonadiabatic and QED corrections.

Determined the s-wave scattering length for singlet H(1s)+H(1s) scattering as 0.2735 a_0.

Abstract

Shape resonances in H$_2$, produced as reaction intermediates in the photolysis of H$_2$S precursor molecules, are measured in a half-collision approach. Before desintegrating into two ground state H atoms, the reaction is quenched by two-photon Doppler-free excitation to the F electronically excited state of H$_2$. For $J=13,15,17,19$ and 21, resonances with lifetimes in the range of nano to milliseconds were observed with an accuracy of 30~MHz (1.4~mK). The experimental resonance positions are found to be in excellent agreement with theoretical predictions when nonadiabatic and quantum electrodynamical corrections are included. This is the first time such effects are observed in collisions between neutral atoms. From the potential energy curve of the H$_2$ molecule, now tested at high accuracy over a wide range of internuclear separations, the s-wave scattering length for singlet H(1s)+H(1s) scattering is determined at $a = 0.2735^{39}_{31}~a_0$.