Chemical stereodynamics of the reaction on the two lowest triplet electronic states

Complete state-resolved non-adiabatic dynamics of the O((3)P) + D2 → OD(X(2)Π) + D reaction

The first quantum-state-resolved distributions over the full range of available product levels are reported for any isotopic variant of the elementary reaction of O((3)P) with molecular hydrogen. A laser-detonation source was used to produce a hyperthermal oxygen-atom beam, which allowed for sufficient collision energy to surmount the reaction barrier. This beam was crossed by a supersonic beam of D2. The nascent OD products were detected by laser-induced fluorescence. OD rotational distributions in vibrational states v' = 0, 1, and 2 at a collision energy of 25 kcal mol(-1) are reported, together with distributions for the dominant product vibrational level, v'= 0, at lower collision energies of 20 and 15 kcal mol(-1). The OD product is highly rotationally excited, to a degree that declines as expected for the higher vibrational levels or for reductions in the collision energy. The measured rovibrational distributions at the highest collision energy are in excellent agreement with previous theoretical predictions based on quantum scattering calculations on the triplet potential energy surfaces developed by Rogers et al. (J. Phys. Chem. A 2000, 104, 2308-2325). However, no significant OD spin-orbit preference was observed, in contrast to the predictions of most existing theoretical models of the non-adiabatic dynamics based on the widely used reduced-dimensional four-state model of Hoffmann and Schatz (J. Chem. Phys. 2000, 113, 9456-9465). Furthermore, a clear observed preference for OD Π(A') Λ-doublet levels is not consistent with a simple extrapolation of the calculated relative reaction cross sections on intermediate surfaces of (3)A' and (3)A″ symmetry.

Product-state-resolved dynamics of the elementary reaction of atomic oxygen with molecular hydrogen, O(³P) + D₂ → OD(X²Π) + D

Elementary three-atom systems provide stringent tests of the accuracy of ab initio theory. One such important reaction, O((3)P) + H2 → OH(X(2)Π) + H, has eluded detailed experimental study because of its high activation barrier. In this reaction, both the ground-state reactant atom and product diatomic molecule have open-shell character, which introduces the intriguing complication of non-Born-Oppenheimer effects in both the entrance and the exit channels. These effects may be probed experimentally in both the fine-structure and the Λ-doublet splittings of the OH product. We have used laser-induced fluorescence to measure OD internal product-state distributions from the analogous reaction of O((3)P) with D2, enabled by a unique high-energy O((3)P) source. We find that the OD (ν' = 0) product is rotationally highly excited, in excellent agreement with earlier theoretical predictions. However, the distributions over the OD(X(2)Π) fine-structure and Λ-doublet states, diagnostic of electronic non-adiabaticity in the reaction, challenge the prevailing theoretical understanding.

STEREODYNAMICS, MASS EFFECT AND DOCKING FROM O(3P) + HD → OH + D AT Ecol = 0.4–1.0eV AND O(3P) + HD → OD + H AT Ecol = 0.5–1.0eV

Quasiclassical Trajectory (QCT) calculation for O(3P) + HD → OH + D and O(3P) + HD → OD + H at E col = 0.4–1.0 eV and 0.5–1.0 eV, respectively, on the lowest PES 1 3A″ of Kuppermann et al. has been done. Distribution p(ϑr) of azimuthal angles between the relative velocity k of the reactants and rotational angular momentum vector j′ of either OH or OD , p(φr) of polar as well as dihedral angles correlating k - k′ -j′, p(ϑr, φr), and PDDCS dependent upon the scattering angle ϑt of either OH , or OD between k and k′ of the reactants and products, respectively, are presented and discussed. The stereodynamics and isotopic mass effects at the smallest possible collision energies 0.4 eV and 0.5 eV for OH and OD , respectively, are significantly different. The significant mass effect with quotient 1/2 of H/D, at the corresponding collision threshold may be applied for the investigation of docking mechanism, drug modification and delivery.