Research Article

Rotational resonances in the H2CO roaming reaction are revealed by detailed correlations

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Science  06 Aug 2020:
eabc4088
DOI: 10.1126/science.abc4088

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Abstract

Since its discovery 16 years ago, “roaming” has become a ubiquitous mechanism in molecular photochemistry. Its general features are now understood, but little detail is known about how the potential energy surface (PES) determines reaction outcomes. We perform detailed experiments on H2CO photodissociation, determining fully correlated quantum state distributions of the H2 and CO products. These experiments reveal previously undetected bimodal CO rotational distributions. Insights from classical trajectory calculations demonstrate these features arise from resonances as the PES directs the reaction into cis and trans O–C–H···H critical geometries, which produce rebound and stripping mechanisms, respectively. These subtle and pervasive effects demonstrate additional complexity in this prototypical roaming reaction, which we expect to be general. They also provide detailed benchmarks for predictive theories of roaming.

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