This article presents theoretical methods for the description of the directional effect of reactant rotation on the reactivity of atom-diatom systems and suggests an experiment that could be used to test theoretical predictions. The theory can be used in conjunction with both quantum reactive scattering and quasiclassical trajectory calculations, and is stated in general terms, which allows it to deal with arbitrary reactant polarizations. The illustrative results obtained for the benchmark H + D2 reaction are also presented and show that under experimentally achievable conditions one can largely control reactive cross sections and product state distributions, while at the same time gaining valuable and at times surprising information on the reaction mechanism.

We present a detailed and quantitative comparison of the quantum mechanical ͑QM͒ and quasiclassical ͑QCT͒ descriptions of the stereodynamics of elementary chemical reactions. Analogous formulations of the QM and QCT k-kЈ-jЈ vector correlation in atom-diatom reactions have been derived and shown to be equivalent in the correspondence principle limit. The comparison between the results obtained from the application of the QM and QCT methodologies to the HϩD 2 (vϭ0, jϭ0)→HD(vЈ, jЈ)ϩD reaction at a collision energy of 1.29 eV renders an almost quantitative agreement.

Reaction of CuX2(X-=Cl- or Br-) with 2 molar equivalents of 3[5]-(2,4,6-trimethylphenyl)pyrazole (HpzMes) in MeOH in the presence of NaOH yields [Cu3X(HpzMes)2(micro-pzMes)3(micro3-OMe)]X (X-=Cl- or Br-). Crystal structures of these compounds show almost identical triangles of Cu(II) ions, centred by a triply bridging methoxide ligand and with three edge-bridging pyrazolide groups. The mesityl substituents on the bridging pyrazolide ligands are arranged in HT, HH, TT fashion. chi(M)T for both compounds decreases steadily with decreasing temperature, reaching 0.40 cm(3) mol(-1) K at 70 K before decreasing further below 40 K. This low temperature behaviour could not be interpreted using conventional superexchange Hamiltonians, but was reproduced by an alternative model that incorporated an additional antisymmetric exchange term. This interpretation was confirmed by the Q-band EPR spectra of the two compounds. NMR experiments show that the structures of these compounds are not retained in solution, in contrast to other closely related tricopper compounds. These are the first examples of triangular Cu(II) compounds bearing a [Cu3micro3-OR)]5+(R is not equal to H) core motif, and the first triangular compounds showing antisymmetric exchange to have been analysed by both susceptibility and EPR measurements.

We have used density matrix techniques and angular momentum algebra to obtain quantum–mechanical equations describing the dynamical stereochemistry of the atom–diatom reaction A+BC⇌AB+C. The relative motions of reagents and products are specified by four vectors: rotational angular momenta of diatomic molecules and relative velocities of reagents and products. Our equations show how the correlations between the spatial distributions of these four vectors are related to the scattering matrix determined in quantum scattering calculations. We present three different expressions for the four-vectors correlation. One of them is appropriate to the helicity representation of the scattering matrix, while the others are appropriate to the orbital angular momentum representation with either space-fixed or body-fixed reference frames. The formulation adopted allows for a rigorous comparison between theory and experiment. It takes mixed quantum–mechanical states and unobserved quantum-numbers into account, and all vector distributions are expressed in terms of measurable quantities (scattering angles and polarization moments of rotational angular momenta). Explicit expressions for most of the lower-order vector correlations obtained by direct reduction of the four-vectors correlation formulas are also presented.

We present results of quantum calculations we have performed on the title reaction in order to study its stereodynamics at collision energies of 0.54 and 1.29 eV. Our theoretical model is based on a representation where directional properties are expressed in terms of real rotational polarization moments instead of magnetic quantum numbers. We analyze the physical meaning of rotational polarization moments and show that, when defined as in the present work, these quantities directly describe the reaction stereodynamics in terms of intuitive chemical concepts related to preferences in the reaction mechanism for particular planes and senses of molecular rotation. Using this interpretation, we identify two distinct regimes for the stereodynamics of the title reaction, observed when HD is formed with low or high rotational excitation. We also identify relevant characteristics of both regimes: ͑i͒ the existence and location of preferred planes and senses of molecular rotation, ͑ii͒ correlations between these preferences, the scattering angle and the reaction probability, and ͑iii͒ their dependence on the collision energy.