Potential energy surfaces and reaction dynamics studies of small triatomic systems: oxygen + hydrogen, hydroxide + hydrogen and hydroxide + deuterium.

摘要

This dissertation is focused on the interaction of open-shell atoms and molecules. We have studied the systems in the title by means of electronic structure and statistical reaction dynamics methods.;We present an ab initio study of the O(3P) + H2 system. In particular, we have calculated potential energy surfaces for the van der Waals region of the interaction and derived and calculated the spin-orbit coupling matrix in the diabatic representation.;The rest of the dissertation is comprised of statistical, coupled-states dynamics studies. Cross sections are calculated by the coupled-states (CS) statistical method including the full open-shell character of the systems. All electronic and spin-orbit couplings are included.;We report state-to-state and overall thermal rate constants for the isotope exchange DS2 +OHI2I →ODI2I +HS2 for 0 K< T < 500 K. We predict a reaction rate constant of 14.22 x 10-11 cm 3 molecule-1 s-1 at T = 100 K and 10.78 x 10-11 cm3 molecule-1 s-1 at T = 300 K. At lower temperatures, ( T ≃ 50 K), the value rises to k(T) = 15 x 10-11 cm3 molecule-1 s -1. A negative temperature dependence in the rate constant is observed. The state-resolved cross sections and rate-constants predict a significant propensity toward formation of the OD II(A') Lambda-doublet level and the ground spin-orbit manifold, F1.;This dissertation is also concerned with the study of vibrational and rotational relaxation of OH(2II) by collision with H atoms. Four potential energy surfaces (PESs) (1,3A' and 1,3A") describe the interaction of OH( X2II) with H atoms. Of these, three are repulsive, while one (1A') correlates with the deep H 2O well. Consequently, rotationally- and ro-vibrationally-inelastic scattering of OH in collisions with H can occur by scattering on the repulsive PESs, in a manner similar to the inelastic scattering of OH by noble gas atoms, or by collisions which enter the H2O well and then re-emerge. We report state-to-state cross sections and thermal rate constants for the collisions. At 300 K, we predict large (≈ 1 x 10-10 cm 3 molecule-1 s-1) vibrational relaxation rates out of both v=2 and v=1, comparable to earlier experimental observations.;This surprisingly fast relaxation results from capture into the H 2O complex. There also exists a significant propensity toward formation of OH in the II(A') Lambda-doublet level. We also report state-resolved cross sections and rate constants for rotational excitation within the OH v=0 manifold. Collisional excitation from the F1 to the F2 spin-orbit manifold leads to an inverted Lambda-doublet population.