https://phys.org/news/2018-07-caffeine-clues-ultra-transient-positive-migration.html > Since the advent of ultra-short laser sources—which operate in the attosecond range—this theory can now be put to the test experimentally. This is because the time scale in which energy absorption by electrons takes place now persists long enough to be observed in experiments. Chemical reactions occurring at specific sites in the caffeine molecule are difficult to realise with longer laser pulses because the heat quickly destroys all site-specific information imprinted by the laser pulse. > The authors find that the observed dynamics for positive charges alongside the backbone of the caffeine molecule depend on the timing of the laser pulse. What is more, the dynamics of the positive charges' migration is governed by the fact that they are inter-related and by the complex interplay between several ionisation channels. Explore further: The pho­to­elec­tric ef­fect in stereo