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Published online: 12 November 2008 | doi:10.1038/nchina.2008.267

Quantum mechanics: Beyond the Born supremacy

Tim Reid

Introduction

It is very difficult to calculate the energy and wavefunction of a molecule. To do so, researchers usually simplify the Schrödinger equation of quantum mechanics by using the 'Born–Oppenheimer approximation'. An international team led by Xueming Yang and Donghui Zhang at the Chinese Academy of Sciences in Dalian, Daiqian Xie at Nanjing University and Millard Alexander at University of Maryland¹ have justified this approximation experimentally, by closely monitoring the reaction of chlorine and hydrogen.

The Born–Oppenheimer approximation breaks the wavefunction problem into separate calculations for the electrons and atomic nuclei in the molecule. However, it ignores the phenomenon of spin-orbit coupling — the interaction of an electron's spin with its motion around a nucleus.

Yang and co-workers crossed molecular beams of chlorine atoms and hydrogen molecules to observe the formation of hydrochloric acid, one of the most widely studied reactions in chemistry. They monitored the reactivity of normal chlorine atoms and those in an excited spin-orbit state, and found that the excited atoms, which are not covered by the Born–Oppenheimer approximation, did not contribute much to the reaction.

The experimental results closely match quantum scattering calculations. These findings make possible investigation of the extent of phenomena outside the Born–Oppenheimer approximation in more complex chemical reactions.

The authors of this work are from:
State Key Laboratory of Molecular Reaction Dynamics, Dalian Institute of Chemical Physics, Chinese Academy of Sciences, Dalian, China; Institute of Theoretical and Computational Chemistry, Key Laboratory of Mesoscopic Chemistry, Ministry of Education, School of Chemistry and Chemical Engineering, Nanjing University, Nanjing, China; Division of Chemistry and Biological Chemistry, School of Physical and Mathematical Sciences, Nanyang Technological University, Singapore; School of Physical and Mathematical Sciences, Nanyang Technological University, Singapore; Institute für Theoretische Chemie, Universität Stuttgart, Stuttgart, Germany; Department of Chemistry and Biochemistry and Institute for Physical Sciences and Technology, University of Maryland, USA.

Reference

1. Wang, X. et al. The extent of non–Born-Oppenheimer coupling in the reaction of Cl(²P) with para-H₂. Science 322, 573–576 (2008).  | Article | PubMed | ChemPort |