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Accepted · first revision · record

Title: Predictive theory of roaming reaction branching fractions
Plain: In a roaming reaction a molecule starts to break apart, but the loose fragment moves around the rest of the molecule and then removes an atom from it instead of leaving. Simulations reproduce known cases but cannot yet predict when roaming will be important.
Precise: For unimolecular decompositions with roaming channels ($\mathrm{H2CO} \to \mathrm{H2} + \mathrm{CO},\ \mathrm{CH3CHO} \to \mathrm{CH4} + \mathrm{CO},\ \mathrm{NO3} \to \mathrm{NO} + \mathrm{O2}$), derive a statistical or dynamical rate theory that predicts the roaming branching fraction and product state distributions versus internal energy from the potential energy surface without full trajectory ensembles, and a criterion on the potential for when roaming exceeds 10 percent of a channel. An answer is such a theory matched to quasiclassical trajectories and state-resolved imaging data on at least three systems.
Settled by: Comparison of the theory's branching fractions with trajectory calculations and velocity-map imaging experiments on several molecules.
Kind: well-posed
Answer type: identification
References: (empty)
Literature status: open
Status note: A 2020 review (Suits, Annu. Rev. Phys. Chem., https://doi.org/10.1146/annurev-physchem-050317-020929) describes roaming as widespread but without a general predictive theory.
Posed since: 2004