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Benjamin McCall

Professor of Chemistry
Professor of Astronomy
Department Affiliate of Physics

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Professor McCall received his B.S. degree in Chemistry from the California Institute of Technology in 1995 and a joint Ph.D. in Chemistry and Astronomy & Astrophysics from the University of Chicago in 2001. He was then a postdoctoral fellow at the University of California at Berkeley. He joined the University of Illinois faculty in 2004.


  • astrochemistry
  • observational spectroscopy of interstellar molecules
  • laboratory spectroscopy

Research Description

The realm of most traditional areas of chemistry is the Earth, which consists of "only" ~10^50 molecules. However, there are ~10^66 molecules in the Milky Way galaxy, which makes the study of Earth's chemistry seem like a small part of the overall picture. Our research is in the emerging field of "astrochemistry," the study of molecules of astronomical importance.

Molecular Ion Spectroscopy. Molecular ions are rare on Earth because they are highly reactive, and consequently they are challenging to study in the laboratory. However, their reactivity makes molecular ions essential for the chemistry at the low densities (~100 cm^-3) and temperatures (~30 K) of interstellar space. In fact, there are ~10,000 times more CH5+ molecules in the Milky Way than there are all molecules on Earth. We are developing cutting-edge laboratory techniques for the laser spectroscopic study of molecular ions in the gas phase. This involves combining supersonic expansions (which produce cold molecular ions) with ion-beam techniques (to separate the ions from the neutrals) and ultra-sensitive spectroscopic methods (which will approach the limit of single-molecule absorption spectroscopy). This powerful combination promises to usher in a new era in molecular ion spectroscopy.

Structure of Carbocations. We are particularly interested in studying the structure and intramolecular dynamics of carbocations such as CH5+ and C6H7+. These molecules not only play key roles in astrochemistry, but they also serve as reactive intermediates in organic chemistry (SN1 reactions and electrophilic aromatic substitution reactions). Such molecules are fundamentally interesting because they violate the "rules" of chemical bonding (carbon is only supposed to make four bonds, not five). A close interplay between spectroscopic experiments and theoretical calculations will be needed to achieve a full quantum-mechanical understanding of molecular ions such as these.

Observational Astrochemistry. With laboratory spectra obtained in the gas-phase at low temperatures in hand, we can use the techniques of astronomical spectroscopy to measure the concentrations of molecular ions (and neutral molecules) in the interstellar medium using powerful ground-based and space-based telescopes. The observed concentrations can then be interpreted using models based on chemical kinetics to serve as a remote probe of both the chemical and physical conditions in interstellar clouds. There are myriad unsolved mysteries in this young and highly interdisciplinary field!

Distinctions / Awards

  • University Scholar
  • Helen Corley Petit Scholar, College of LAS
  • Camille Dreyfus Teacher-Scholar Award
  • Dean's Teaching Fellowship, College of LAS
  • Sloan Research Fellowship, Alfred P. Sloan Foundation
  • Coblentz Award for Molecular Spectroscopy
  • Cottrell Scholar Award, Research Corporation
  • Air Force Young Investigator Award
  • David and Lucile Packard Fellowship
  • Presidential Early Career Award for Scientists and Engineers (PECASE)
  • NSF CAREER Award
  • Miller Research Fellow
  • Fannie and John Hertz Predoctoral Fellow