Bimolecular collision outcomes on multidimensional potential energy surfaces: infrared spectroscopy and activation of NO–alkane collision complexes

Abstract

In bimolecular collisions between open-shell radicals and increasingly-larger alkanes, the relative impact configurations open the possibility of reactive and nonreactive outcomes that are isomer specific. To model the interaction potential between molecular scattering partners, observables are needed from experiments that can quantify both the initial molecular orientations and internal energies on multidimensional potential energy surfaces. Recent work by our group demonstrated that upon infrared (IR) excitation, the dynamics of the nitric oxide–methane collision complex (NO–CH₄) are dependent on the initial monomer geometries, as small changes in configuration substantially affect the energies, electronic couplings, and predissociation pathways due to the Jahn–Teller effect. This study focuses on the isomer-specific scattering mechanisms between NO and ethane (C₂H₆), encoded in the spectroscopic and dynamical signatures of the NO–C₂H₆ collision complex. IR action spectroscopy with 1 + 1 resonance-enhanced multiphoton ionization of NO products was employed to characterize the fundamental CH stretch transitions of NO–C₂H₆, as well as to initiate the nonreactive decay mechanisms of the complex. Furthermore, velocity map imaging (VMI) was utilized to explore the dynamics prior to and following IR excitation of NO–C₂H₆, imprinted on the NO photoproducts. This work compares the dynamics from NO–C₂H₆ and NO–CH₄ vibrational predissociation, in which substantial differences are observed in the energy exchange mechanisms during the evolution of the collision complexes to products.