Ultrafast studies of chemical reactions and other molecular dynamics typically rely on the use of femtosecond and, more recently, attosecond light sources to probe the reaction. For example, a short laser pump pulse can first be used to trigger a light-induced reaction in a molecular sample, with a probe pulse following to characterize the results. Now, two researchers at the University of Toronto (Toronto, ON, Canada), Hazem Daoud and R. J. Dwayne Miller, propose a different and quite radical approach: accelerate the sample specimen itself to relativistic speed to slow its internal clock down, enabling finer-grained temporal measurement to be made. To a nonmoving observer, the “internal clock” of a sample moving at velocity v slows down by a factor of (1 - v2/c2)1/2, where c is the velocity of light; thus, the time resolution of an experiment can be a function of the sample’s energy.
The researchers say that small samples could be accelerated in a cyclotron or synchrotron and then be studied at a fixed energy, with a pump light pulse and probe light pulse directed parallel to each other and perpendicular to the specimen’s direction of motion. For example, the Large Hadron Collider at CERN can accelerate lead ions to a collision energy of 5 TeV. The researchers say that a hydronium molecule (H3O+), for example, when accelerated to 1.8 TeV, would be slowed down in time by a factor of 100, thus increasing time resolution by a factor of 100; when accelerated to 18 TeV, the increase in time resolution would be 1000-fold. Reference: H. Daoud and R. J. Dwayne Miller, J. Chem. Phys. (2021); https://doi.org/10.1063/5.0037862.