Beckman Fellow 2007-08

Benjamin McCall



Carbocations (positively charged hydrocarbon molecules) are fundamental and ubiquitous in many different types of organic chemical reactions. They drive the production of prebiological molecules in the low-density and low-temperature environment of interstellar clouds, and they also play a key role in combustion chemistry.

Despite their importance, even simple carbocations such as CH5+ are poorly understood because of their nonclassical bonding (3-center, 2-electron) and complex intramolecular dynamics, including facile tunneling. The traditional tool for understanding the structure and behavior of molecules is spectroscopy of the bare molecules in the gas phase at very high spectral resolution. However, this technique has been only partially successful when applied to complex carbocations because of various technical limitations.

During his Center appointment, Professor McCall plans to develop a new laboratory technique that will permit the detailed spectroscopic study of molecular ions, with a special emphasis on complex carbocations. His group’s approach combines several well-established techniques in a novel way they call SCRIBES. Using this approach, the group can study carbocations at very low temperatures (comparable to the temperatures in interstellar space) in the absence of any uncharged molecules (which otherwise confuse the spectrum). The new approach is expected to open up the world of carbocations to detailed spectroscopic study. Results should yield a better understanding of these fundamental molecules and reveal the spectroscopic “fingerprints” needed to detect them in interstellar space.