Dynamical resonances in chemical reactions

RESEARCH HIGHLIGHTS Guo251
Chuan He1,2
1Department of Chemistry and Institute for Biophysical Dynamics,Howard Hughes Medical Institute,The University of Chicago,USA;
2College of Chemistry and Molecular Engineering, Peking University,China
E-mail:chuanhe@ REFERENCES
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doi:10.1093/nsr/nwv030
Advance access publication8June2015
CHEMISTRY
Dynamical resonances in chemical reactions Hua Guo
Gas-phase chemical reactions occur when one reactant collides with an-other followed by rearrangements of the atoms in the activated complex. This process is typically described by the reaction coordinate leading from the reactants to products via a transition state.In general,the transition state is only a whistle-stop for the reactive flux.However,an activated complex can sometimes be transiently trapped in the transition-state region as metastable quantum states.Such dynamical res-onances can profoundly influence the dynamics of a chemical reaction.As a result,it has attracted much attention in the field of chemical dynamics over the past30years.Although signatures of dynamical resonances have been detected in several reactions[1–4],only the F+H2(HD)resonances have been elucidated[1–3].
It is thus exciting when a research team led by Profs Xueming Yang and Dong Hui Zhang in State Key Labora-tory of Molecular Reaction Dynamics, Dalian Institute of Chemical Physics, Chinese Academy of Sciences,un-equivocally proved the existence of dynamical resonances in the Cl+HD (v=1)→DCl+H reaction and elucidate them clearly through the state-of-the-art crossed molecular beams experiment and quantum dynamics calculations[5].Experimentally,the first application of stimulated Raman pump-ing of HD molecules to the vibrationally excited v=1state in a crossed molecu-
lar beams study,in combination with the
so-called differential cross-sections back-
ward scattering spectroscopy method de-
veloped in their own laboratory,is push-
ing the envelope to a new level of sophisti-
plementing the experiment,
quantum dynamical calculations were
performed on the most accurate global
potential energy surface and helped to
gain mechanistic insights.
Two distinct peaks for the DCl
(v=1)product detected in the back-
ward scattering direction were
attributed
Figure1.Illustration of the formation of dynamical resonances in the Cl+HD→DCl+H reaction.
to dynamical resonances by theory.As
shown in Fig.1,the interaction between
H and DCl in the transition-state re-
gion softens the DCl bond,manifest-
ing by a lower vibrational frequency,and
more importantly larger anharmonicity.
The latter considerably lowers the DCl
energy levels for vibrationally excited
states,leading to a shallow well on the
DCl(v DCl=2)–H vibrational adiabatic
potential,which supports resonances.
Hence,the physical picture for these res-
onances cannot be obtained with the
widely used normal mode analysis.They。