Molecular Imaging: from Coulomb Explosions to Modelling

Speaker: David Babalola (MCSC)

Abstract: The advent of a laser has improved or made many areas of research possible; and one research area that has benefited immensely is molecular chemistry. In particular, the determination of molecular structure with Coulomb explosion imaging (CEI), and, by sequencing this process, insight into molecular reaction dynamics by constructing a so-called “molecular movie.”  The determination of molecular structure is an interesting adventure, but not without its difficulties. Some of the impediments to determining structure with CEI will be detailed.
In this talk, I will discuss how the Coulomb explosion (CE) images are created with a velocity map imaging (VMI) spectrometer.  This device is characterized by a specialized electrostatic lens which focusses ions with the same velocity to the same spot on the detector, independent of where the ion is created, thereby eliminating the natural blurring due to the finite size of the overlap of the molecular beam and the laser beam that strips the valence electrons.  I will present the model behind the focusing ability of the electrostatic lens.

With the electrostatic lens configuration in the spectrometer, the 3D velocity distribution of the scattered fragments, also called a Newton sphere, is mapped onto a detector.  To better understand the CE problem, an asymptotic analysis of the non-linear, multivariate differential equation governing the CE phenomenon is performed. The resulting multi-scale sub-problems, and corresponding simulations are in good agreement with the experimental results. In addition, and with time permitting, I will discuss complementary ways that the data from a VMI is analyzed.  Finally, I will present an attempt to reconstruct some molecules using an inverse kinematics approach.