Classical trajectory and statistical adiabatic channel study of the dynamics of capture and unimolecular bond fission. V. Valence interactions between two linear rotors

Abstract

The combination of two linear rotors forming linear or nonlinear adducts is treated using standardized valence potentials. Classical trajectory (CT) and statistical adiabatic channel (SACM) calculations are used for the calculation of thermal capture rate constants. At very low temperatures, only SACM applies. At intermediate temperatures SACM and CT approach each other; however, Landau–Zener-type multiple crossings of adiabatic channel potentials introduce local nonadiabaticity which has to be accounted for. The high-temperature transition from globally adiabatic to nonadiabatic (sudden) dynamics is studied by CT. Thermal rigidity factors, accounting for the influence of the anisotropy of the potential on the capture rate constant, are expressed in simple analytical form which facilitates practical applications. The present work complements similar studies on the addition of atoms to linear molecules in standardized valence potentials (part IV of this series).

Classical Trajectory and Statistical Adiabatic Channel Study of the Dynamics of Capture and Unimolecular Bond Fission. VII. Thermal Capture and Specific Rate Constants k(E,J) for the Dissociation of Molecular Ions

“…The transitional mode potentials considered in [1][2][3][4][5][6] were partly of "mixed" (ion-permanent plus induced dipole [1], ion-quadrupole plus induced dipole [2], dipole-dipole plus dispersion [3]), partly of "homogeneous" valence character [4,5]. The former potentials [1][2][3] were characterized by regions of differing anisotropies while the latter [4,5] had uniform anisotropies.…”

“…In the previous articles of this series [1][2][3][4][5][6], we have treated unimolecular bond fission and the reverse association reactions by a combination of the statistical adiabatic channel model (SACM) and classical trajectory (CT) calculations. The dissociative separation of two species and the reverse associative capture process forming a bound adduct were followed, in reduced dimensionality, by explicitly treating the dynamics of the transitional modes (external rotations of the fragments) while conserved modes (internal modes of the fragments) were handled adiabatically.…”

“…The dissociative separation of two species and the reverse associative capture process forming a bound adduct were followed, in reduced dimensionality, by explicitly treating the dynamics of the transitional modes (external rotations of the fragments) while conserved modes (internal modes of the fragments) were handled adiabatically. The SACM/CT approach is able to establish a direct link between the potential energy surfaces (PESs) and thermal rate constants for capture kcap(T) (or the corresponding high pressure rate constants for recombination and the reverse dissociation) such as demonstrated in [1][2][3][4][5]. In addition, specific rate constants k(E, J) for unimolecular bond fissions as a function of the energy E and the angular momentum (quantum number J) can be derived in a way which is consistent with the thermal capture rate constants, see [6].…”

“…For this reason, we have calculated thermal capture rate constants [1][2][3][4][5] and the corresponding specific rate constants [6] for a series of interfragment potentials such as ion-dipole [1], ion-quadrupole [2], dipoledipole [3], atom-linear rotor model valence [4], and linear rotor-linear rotor model valence [5] potentials. By using such model potentials, insight into what specifically controls the reactivity is developed.…”

“…and kc, 5 (T) from rigid activated complex Rice-Ramsperger-Kassel-Marcus (RRKM) theory are compared with the SACM/CT treatment and with experimental results. The Massey parameters of the transitional mode dynamics, for the systems considered, are smaller than unity such that their dynamics is nonadiabatic while the dynamics of the conserved modes is adiabatic.…”