Big Molecules’ Little Electrons Probed

A new spectroscopic technique allows scientists to probe the laser-driven attosecond-scale motions of electrons in large molecules (Science, DOI: 10.1126/science1212896). The motions of electrons in strong laser fields underlie the emerging field of attosecond science. But until now, experiments that resolve ultrafast electron motions in strong laser fields have been accomplished only with single atoms or small molecules. Larger molecules, which have more electrons, present a more challenging problem. Now, Albert Stolow, Andrey E. Boguslavskiy, Jochen Mikosch, and colleagues of the National Research Council of Canada have used laser pulses to generate strong electric fields that singly ionize linear n-butane and 1,3-butadiene. The researchers observed spectral characteristics of both the ionized molecule and the free electron. From this method, which they call channel-resolved above-threshold ionization, they were able to identify the specific electron orbitals that participated. This work extends attosecond science toward large molecules and sets the stage for observing more complex phenomena in strong laser fields, the researchers note. Understanding the dynamics of attosecond-scale electronic motion could allow scientists to explore ultrafast molecular charge and energy transport, says SLAC National Accelerator Laboratory physicist Markus Gühr in a commentary.