Chemical reaction dynamics with molecular beams

Abstract

This review describes advances which have occurred during the past decade in chemical reaction dynamics using crossed molecular beams. After a brief historical introduction, advances in the generation and state selection of beams of reactants, and in the schemes for product detection, which are at the basis of our increased ability to measure state-averaged and state-resolved reactive differential cross sections in crossed beam experiments, are described. The novel couplings of laser and synchrotron radiation to these experiments are noted. A selection of case studies are considered in some detail, to exemplify recent improvements in our understanding of gas-phase neutral reaction dynamics. The examples include prototype reactions involving three-atom and four-atom systems, and the results are discussed in the light of the most recent, synergistic, theoretical developments for treating both the potential energy surfaces and the reaction dynamics. Progress made in studies of reactions of molecular radicals and of chemically important atoms, such as carbon, nitrogen, and oxygen, with polyatomic molecules, as made possible by recent developments in the classic crossed beam technique with mass spectrometric detection, is emphasized. Some complementary techniques that recently have contributed to our understanding of chemical reactivity are also described briefly.

A fully state- and angle-resolved study of the H+HD→D+H2 reaction: Comparison of a molecular beam experiment to ab initio quantum reaction dynamics

“…We also note there have been other important recent advances in the molecular beam methodology that have allowed improvements in the resolution and facility of reactive scattering data. 5,[7][8][9] On the theory side, a potential energy surface of Boothroyd et al, 10 the BKMP2-PES, is apparently globally accurate to within 30 cm Ϫ1 , which is likely to be sufficient to model the reaction dynamics. Anderson and co-workers have recently developed an even more accurate surface.…”

A quasiclassical trajectory and quantum mechanical study of the O(1D) + D2reaction dynamics. Comparison with high resolution molecular beam experiments

“…Dynamical calculations indicate that the reaction over the ground state PES takes place via an insertion mechanism that leads to products isotropically scattered and distributed in a near statistical way over the available internal energy levels. However, reaction over the excited 1 1 A 00 PES proceeds via an abstraction mechanism, yielding mostly backward scattering (with respect to the incoming atom) and with vibrationally hot and rotationally cold product state distributions. The reaction over the 2 1 A 0 surface, which does not correlate with ground state products, can take place by means of non-adiabatic coupling through a conical intersection with the ground 1 1 A 0 state.…”

“…However, reaction over the excited 1 1 A 00 PES proceeds via an abstraction mechanism, yielding mostly backward scattering (with respect to the incoming atom) and with vibrationally hot and rotationally cold product state distributions. The reaction over the 2 1 A 0 surface, which does not correlate with ground state products, can take place by means of non-adiabatic coupling through a conical intersection with the ground 1 1 A 0 state. The products from this channel would exhibit a mixture of the characteristics of the insertion and abstraction mechanisms.…”

Kinematically complete reaction dynamics of slow ions

“…To study the quantum dynamics of molecular collisions and reactions, kinematically complete experiments with crossed molecular beams are an invaluable tool [1]. Such experiments yield energy and angle-differential scattering cross sections and allow one to unravel quantum-state specific dynamics of complex few-body scattering problems.…”