Ballistic Energy Transport in Molecules

Tulane University, New Orleans LA

Investigators

Abstract

With this award, the Chemical Structure, Dynamics and Mechanisms (CSDM-A) Program in the Division of Chemistry is funding Professors Igor Rubtsov and Alexander Burin of Tulane University to investigate unusually rapid movement of energy in molecules, so-called "ballistic energy transport." Most often energy (as heat) is transported slowly through materials through the random motion of electrons and atoms making up the material (this is called "thermal diffusion"). Professor Rubtsov's research group has discovered systems where energy deposited in long molecules is rapidly transferred to distant locations, not unlike a bullet or projectile. This anomalous transfer of energy may help scientists discover new materials with improved thermal transport properties. The graduate and undergraduate students working on this project are receiving training in optical science, laser spectroscopy and quantum theory. The PI and co-PI participate in a number of educational activities on their campus, including the Tulane Louis Stokes Louisiana Alliance for Minority Participation (LS-LAMP) Summer Undergraduate Research Training Program, which provides undergraduate students from groups underrepresented in science with authentic research experiences. Professors Igor Rubtsov and Alexander Burin and their respective research groups are combining ultrafast laser spectroscopy (relaxation-assisted two-dimensional infrared spectroscopy (2DIR)) with theoretical modeling to develop a better understanding of how the very rapid energy transport over molecularly-significant distances occurs. Some of the questions that these scientists hope to answer include: What are the main factors determining the speed of ballistic transport and how to increase its efficiency? How do the transport parameters, such as efficiency, speed, band selection, and cooling rate, depend on the environment and temperature? Can these transport parameters be controlled by external stimuli and how to design molecules for such control? Can the ballistic transport be efficient against the direction of thermal gradient? Among the factors affecting transport to be examined are the primary and secondary chain structure, chain architecture, the nature and energy of the source vibrational mode, and the temperature. These studies are identifying the most likely transport mechanisms and, as such, will likely suggest ways of reducing losses for ballistic energy transport and directing energy to specific targets. The ballistic transport mechanism is considered as a principal component of energy transport in molecules, especially for molecules featuring functional groups with repeating units, which are very common. These studies are helping us understanding how to use the ballistic transport and how to manipulate its outcome. Establishing the fundamental principles needed to make the process either fast and efficient or slow and inefficient could impact a broad class of problems that take center stage in nanoscience and molecular electronics. In addition to the aforementioned training and outreach activities, this project includes the the designing of a novel undergraduate course that incorporates the knowledge obtained in the program and implements an experimental exercise on 2DIR spectroscopy. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.