title: Roaming-mediated ultrafast isomerization of geminal tri-bromides in the gas and liquid phases.
abstract: 'Roaming' is a new and unusual class of reaction mechanism that has recently been discovered in unimolecular dissociation reactions of isolated molecules in the gas phase. It is characterized by frustrated bond cleavage, after which the two incipient fragments 'roam' on a flat region of the potential energy surface before reacting with one another. Here, we provide evidence that supports roaming in the liquid phase. We are now able to explain previous solution-phase experiments by comparing them with new ultrafast transient absorption data showing the photoisomerization of gas-phase CHBr3. We see that, upon S0-S1 excitation, gas-phase CHBr3 isomerizes within 100 fs into the BrHCBr-Br species, which is identical to what has been observed in solution. Similar sub-100 fs isomerization is now also observed for BBr3 and PBr3 in solution upon S1 excitation. Quantum chemical simulations of XBr3 (X = B, P or CH) suggest that photochemical reactivity in all three cases studied is governed by S1/S0 conical intersections and can best be described as occurring through roaming-mediated pathways.
authors.affiliation: Department of Chemistry and the Center for Photochemical Sciences, Bowling Green State University, Bowling Green, Ohio 43403, USA.
authors.forename: Andrey S
authors.initials: AS
authors.lastname: Mereshchenko
authors.affiliation: Department of Chemistry and the Center for Photochemical Sciences, Bowling Green State University, Bowling Green, Ohio 43403, USA.
authors.forename: Evgeniia V
authors.initials: EV
authors.lastname: Butaeva
authors.affiliation: Department of Chemistry and the Center for Photochemical Sciences, Bowling Green State University, Bowling Green, Ohio 43403, USA.
authors.forename: Veniamin A
authors.initials: VA
authors.lastname: Borin
authors.affiliation: Department of Chemistry and the Center for Photochemical Sciences, Bowling Green State University, Bowling Green, Ohio 43403, USA.
authors.forename: Anna
authors.initials: A
authors.lastname: Eyzips
authors.affiliation: Department of Chemistry and the Center for Photochemical Sciences, Bowling Green State University, Bowling Green, Ohio 43403, USA.
authors.forename: Alexander N
authors.initials: AN
authors.lastname: Tarnovsky