Abstract
It has long been known that there is a conical intersection (CI) between the ground and first excited electronic state in the H3 system. Its associated geometric phase (GP) effect has been theoretically predicted to exist below the CI since a long time. However, the experimental evidence has not been established yet and its dynamical origin is waiting to be elucidated. Here we report a combined crossed molecular beam and quantum reactive scattering dynamics study of the H+HD → H2+D reaction at 2.28 eV, which is well below the CI. The GP effect is clearly identified by the observation of distinct oscillations in the differential cross section around the forward direction. Quantum dynamics theory reveals that the GP effect arises from the phase alteration of a small part of the wave function, which corresponds to an unusual roaming-like abstraction pathway, as revealed by quasi-classical trajectory calculations.
Highlights
It has long been known that there is a conical intersection (CI) between the ground and first excited electronic state in the H3 system
For a molecular system with a CI, the theoretical treatment in the adiabatic picture requires the inclusion of the geometric phase (GP) to make sure that at each nuclear geometry, the total wave function can be single-valued, the nuclear wave function is localized away from the region of the CI
The H+HD→H2+D reactive scattering experiment is carried out using a crossed molecular beam (CMB) apparatus with a velocity map imaging (VMI) detector at the collision energy of 2.28 eV
Summary
It has long been known that there is a conical intersection (CI) between the ground and first excited electronic state in the H3 system. The increased number of degrees of freedom and electronic states leads to the general presence of CIs in various molecular photoinduced chemical dynamics processes involving electronically excited states, where CIs play a very important role[13]. H+H2 is one of the most important chemical reactions since it can be accurately described with current quantum theoretical methods It exhibits a typical D3h CI between the ground and first excited electronic states at equilateral triangle geometries, corresponding to the total energy of about 2.75 eV. Using the ground adiabatic potential energy surface (PES), product state-resolved integral and differential cross sections (DCS) for the H+H2 reaction and its isotopologues without consideration of the GP were first reported in 198814,15. It was found that the adiabatic quantum dynamics predictions without the GP
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