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Photochemistry

Scrambled by the Sun?

Nature Chemistry volume 3, pages 423–424 (2011)Cite this article

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Isotopic labelling is widely used to unravel reaction mechanisms, but are conclusions from such studies always robust? Now, studies on the photolysis of CD3CHO reveal extensive isotopic scrambling before dissociation, which could have implications for our mechanistic understanding of some key aspects of atmospheric photochemistry.

The decay of energized gas-phase molecules has long fascinated chemists. Our understanding of such processes developed through the efforts of pioneers like Lindemann, Eyring, Evans and Polanyi, and Rice, Ramsberger, Kassel and Marcus. The success of the statistical frameworks that they introduced for understanding chemical kinetics means that transition-state theory now features in almost all physical chemistry textbooks1. Transition-state theory (and its microcanonical counterpart, RRKM theory — named after the later developers mentioned above) invokes two key assumptions: the concept of a dividing surface, passage through which will result in (irreversible) conversion of reactant to product; and ergodicity, which means that energy is randomized rapidly throughout all of a molecule's degrees of freedom in a time that is short compared with the timescale of the reaction. Although not without some (recognized) limitations2, these two assumptions provide the basis for most widely used reaction-rate theories.

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Figure 1: Schematic illustrating the near-threshold photodissociation of CD3CHO (boxed).

References

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Authors and Affiliations

  1. Mike Ashfold and David Glowacki are in the School of Chemistry, University of Bristol, Bristol BS8 1TS, UK.,

    Michael N R Ashfold & David R Glowacki

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  1. Michael N R Ashfold
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  2. David R Glowacki
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Correspondence to Michael N R Ashfold or David R Glowacki.

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Ashfold, M., Glowacki, D. Scrambled by the Sun?. Nature Chem 3, 423–424 (2011). https://doi.org/10.1038/nchem.1058

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