Chemistry at Illinois University of Illinois at Urbana-Champaign

Benjamin J. McCall

Professor of Chemistry and Astronomy
associate head of buildings and services
Affiliate, Department of Physics

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 as an Assistant Professor in Fall 2004. His research interests are in the overlapping areas of high-resolution molecular spectroscopy and interstellar chemistry.


The realm of most traditional areas of chemistry is the Earth, which consists of "only" ~1050 molecules. However, there are ~1066 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!


A. A. Mills, B. M. Siller, and B. J. McCall, "Precision Cavity Enhanced Velocity Modulation Spectroscopy," Chemical Physics Letters,501, 1 (2010).

N. Indriolo, G. A. Blake, M. Goto, T. Usuda, T. Oka, T. R. Geballe, B. D. Fields, and B. J. McCall, "Investigating the Cosmic-Ray Ionization Rate Near the Supernova Remnant IC 443 through H3+ Observations," Astrophysical Journal, 724, 1357 (2010).

H. Kreckel, O. Novotny, K. N. Crabtree, H. Buhr, A. Petrignani, B. A. Tom, R. Thomas, M. H. Berg, D. Bing, M. Grieser, C. Krantz, M. Lestinsky, M. B. Mendes, C. Nordhorn, R. Repnow, J. Stutzel, A. Wolf, and B. J. McCall, "High-Resolution Storage Ring Measurements of the Dissociative Recombination of H3+ Using a Supersonic Expansion Ion Source," Physical Review A, 82, 042715 (2010).

K. N. Crabtree, C. A. Kauffman, and B. J. McCall, "A Modular and Robust Continuous Supersonic Expansion Discharge Source," Review of Scientific Instruments, 81, 086103 (2010).

B. E. Brumfield, J. T. Stewart, S. L. Widicus Weaver, M. D. Escarra, S. S. Howard, C. F. Gmachl, and B. J. McCall, "A Quantum Cascade Laser cw Cavity Ringdown Spectrometer Coupled to a High Temperature Oven Supersonic Expansion Source," Review of Scientific Instruments, 81, 063102 (2010).

B. M. Siller, A. A. Mills, and B. J. McCall, "Cavity Enhanced Velocity Modulation Spectroscopy," Optics Letters, 32, 1266 (2010).

B. A. Tom, A. A. Mills, M. B. Wiczer, K. N. Crabtree, and B. J. McCall, "Development and Characterization of a Source of Rotationally Cold, Enriched para-H3+," Journal of Chemical Physics, 132, 1103 (2010).

B. J. McCall, M. M. Drosback, J. A. Thorburn, D. G. York, S. D. Friedman, L. M. Hobbs, B. L. Rachford, T. P. Snow, P. Sonnentrucker, and D. E. Welty, "Studies of the Diffuse Interstellar Bands. IV. The Nearly Perfect Correlation Between ΛΛ6196.0 and 6613.6," Astrophysical Journal, 708, 1628 (2010).

N. Indriolo, B. D. Fields, and B. J. McCall "The Implications of a High Cosmic-Ray Ionization Rate in Diffuse Interstellar Clouds" Astrophysical Journal (2009), 694, 257-267.>

S. L. Widicus Weaver, D. E. Woon, B. Ruscic and B. J. McCall "Is HO2+ a Detectable Interstellar Molecule?" Astrophysical Journal (2009), 697, 601-609.

B. A. Tom, S. Bhasker, Y. Miyamoto, T. Momose, and B. J. McCall "Producing and Quantifying Enriched Para-H2" Review of Scientific Instruments (2009), 80, 016108.


  • 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
  • Cottrell Scholar Award, Research Corporation
  • Beckman Fellow, Center for Advanced Study
  • 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



Photo of Benjamin J. McCall