Roaming in acetaldehyde

Abstract

We investigate roaming in the photodissociation of acetaldehyde (CH${}_3$CHO), providing insight into the contrasting roaming dynamics observed for this molecule compared to formaldehyde. We carry out trajectory studies for full-dimensional acetaldehyde, supplemented with an analysis of a two degree-of-freedom restricted model and obtain evidence for two distinct roaming pathways. Trajectories exhibit roaming at both shorter (9-11.5 au) and larger (14.5-22.9 au) maximum CH${}_3$-HCO separations, characterized by differing amounts of HCO rotation. No roaming trajectories were found in the intervening gap region. The roaming dynamics near 14.5-22.9 au are well-reproduced by the restricted model and involve passage through a centrifugal barrier, analogous to formaldehyde roaming. However, the shorter-range 9-11.5 au roaming appears unique to acetaldehyde, and is likely facilitated by repulsive interactions absent in the simplified models. Phase space analysis reveals that this additional roaming pathway is inaccessible in the reduced dimensionality system. The findings suggest acetaldehyde's increased propensity for roaming compared to formaldehyde may arise from the presence of multiple distinct roaming mechanisms rather than solely the higher roaming fragment mass.

References in corpus (10)

• Distinguished trajectories in time dependent vector fields
• Multiple Transition States and Roaming in Ion-Molecule Reactions: a Phase Space Perspective
• Roaming dynamics in ion-molecule reactions: phase space reaction pathways and geometrical interpretation
• Phase space barriers and dividing surfaces in the absence of critical points of the potential energy: Application to roaming in ozone
• Binary contraction method for the construction of time-dependent dividing surfaces in driven chemical reactions
• The phase space geometry underlying roaming reaction dynamics
• Using Lagrangian descriptors to uncover invariant structures in Chesnavich's Isokinetic Model with application to roaming
• Influence of mass and potential energy surface geometry on roaming in Chesnavich's CH${}_4^{+}$ model
• Roaming at Constant Kinetic Energy: Chesnavich's Model and the Hamiltonian Isokinetic Thermostat
• Phase space structures causing the reaction rate decrease in the collinear hydrogen exchange reaction