Molecular Movie

Chemical reactions occur at such small scales that we usually only measure their progress indirectly through temperature and pressure changes.  But an international team of scientists has used X-rays to film the evolution of one molecular interaction.

The molecule in the starring role is C₂H₄I₂, which was placed in a solution of liquid methanol (shown as gray spheres).

In the upper-left-hand image, there is the intact molecule with its elemental components:  carbon (green), hydrogen (blue), and iodine (purple).  A laser pulse then excites the molecule, and the aftermath is recorded in the subsequent images (moving clockwise).

First, one of the iodine atoms breaks free from the rest of the molecule.  Shortly after, this "fugitive" recombines with its fellow iodine and ends up pulling it free as well.   The whole sequence of events takes place over the course of a millionth of a second.

The images confirm a theory of how the molecular structure of C₂H₄I₂ changes when excited.

The results were published on July 14 in Science Express, the online counterpart of the journal Science.

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 -- Michael Schirber

Credit: European Synchrotron Radiation Facility