title: Roaming: A Phase Space Perspective.
abstract: In this review we discuss the recently described roaming mechanism for chemical reactions from the point of view of nonlinear dynamical systems in phase space. The recognition of the roaming phenomenon shows the need for further developments in our fundamental understanding of basic reaction dynamics, as is made clear by considering some questions that cut across most studies of roaming: Is the dynamics statistical? Can transition state theory be applied to estimate roaming reaction rates? What role do saddle points on the potential energy surface play in explaining the behavior of roaming trajectories? How do we construct a dividing surface that is appropriate for describing the transformation from reactants to products for roaming trajectories? How should we define the roaming region? We show that the phase space perspective on reaction dynamics provides the setting in which these questions can be properly framed and answered. We illustrate these ideas by considering photodissociation of formaldehyde. The phase-space formulation allows an unambiguous description of all possible reactive events, which also allows us to uncover the phase space mechanism that explains which trajectories roam, as opposed to evolving toward a different reactive event.
authors.affiliation: School of Mathematics, University of Bristol, Bristol BS8 1TW, United Kingdom; email: frederic.mauguiere@bristol.ac.uk , peter.collins@bristol.ac.uk , stephen.wiggins@mac.com.
authors.forename: Frédéric A L
authors.initials: FAL
authors.lastname: Mauguière
authors.affiliation: School of Mathematics, University of Bristol, Bristol BS8 1TW, United Kingdom; email: frederic.mauguiere@bristol.ac.uk , peter.collins@bristol.ac.uk , stephen.wiggins@mac.com.
authors.forename: Peter
authors.initials: P
authors.lastname: Collins
authors.affiliation: Department of Chemistry and Biochemistry, La Salle University, Philadelphia, Pennsylvania 19141; email: kramerz@lasalle.edu.
authors.forename: Zeb C
authors.initials: ZC
authors.lastname: Kramer
authors.affiliation: School of Chemistry, Cardiff University, Cardiff CF10 3AT, United Kingdom; email: carpenterb1@cardiff.ac.uk.
authors.forename: Barry K
authors.initials: BK
authors.lastname: Carpenter
authors.affiliation: Department of Chemistry and Chemical Biology, Baker Laboratory, Cornell University, Ithaca, New York 14853; email: gse1@cornell.edu.
authors.forename: Gregory S
authors.initials: GS
authors.lastname: Ezra
authors.affiliation: Department of Chemistry, University of Crete, Heraklion 700 13, Greece.|Institute of Electronic Structure and Laser, Foundation for Research and Technology-Hellas, Heraklion 711 10, Greece; email: farantos@iesl.forth.gr.
authors.forename: Stavros C
authors.initials: SC
authors.lastname: Farantos
authors.affiliation: School of Mathematics, University of Bristol, Bristol BS8 1TW, United Kingdom; email: frederic.mauguiere@bristol.ac.uk , peter.collins@bristol.ac.uk , stephen.wiggins@mac.com.
authors.forename: Stephen
authors.initials: S
authors.lastname: Wiggins
keywords: dividing surface; normally hyperbolic invariant manifold; periodic orbit; phase space landscape; roaming mechanism; transition state