Inside the Laboratory: The McGuire Group at the Massachusetts Institute of Technology

"Inside the Laboratory" is a joint series with LCGC and Spectroscopy, profiling analytical scientists and their research groups at universities all over the world. This series spotlights the current chromatographic and spectroscopic research their groups are conducting, and the importance of their research in analytical chemistry and specific industries. In this edition of “Inside the Laboratory,” Brett McGuire of the Massachusetts Institute of Technology (MIT) discusses his laboratory’s work in astrochemistry (1). This interview was conducted in conjunction with our preview of the 78^th International Symposium on Molecular Spectroscopy taking place this week (2).

Will Wetzel: Can you provide a brief overview of what your laboratory group is working on?

Brett McGuire: My group is primarily interested in detecting new and more complex molecules in space, understanding just how complex the chemistry can get. We're relatively new, so we've been building up a laboratory, but the instruments we're building are microwave spectrometers to perform rotational spectroscopy. In rotational spectroscopy, we analyze the patterns of light that molecules give off as they tumble freely. These are low-energy transitions, which means that they can be populated even at 10 Kelvin in the interstellar medium. They're also highly separable. The signals from rotational spectroscopy are unique to each molecule. If you change even a single neutron, changing a carbon-12 to a carbon-13, the signals shift by many line widths, meaning that you can trivially distinguish one molecule from another with no ambiguity. This makes it an ideal method to study molecules in cold places in space, where we want to understand what the different molecules are.

We're building primarily microwave spectroscopy instruments at the moment. This is a broadband technique that was invented by Brooks Pate about 15 or 20 years ago that allows us to collect the spectra across a wide range (many gigahertz). Depending on the molecule, we can collect dozens to hundreds to 1000s of rotational transitions all at once. And then, we can use those collected transitions, go through quantum mechanics, fit them to a Hamiltonian, predict all of the other transitions that should be present, and then go and take that data and match it to observations we take with radio telescopes as well to detect molecules in space. We're particularly interested in aromatic and polycyclic aromatic molecules currently. Our instrument here right now can study molecules up to about two rings. We've been studying primarily single and double ring aromatic molecules at the moment. We then work with collaborators, such as Mike McCarthy at the Center for Astrophysics just up the road, because he has more sensitive, cavity-based instruments that are very narrow band and very sensitive, that can study even larger molecules. My group goes up there and uses those instruments as well in collaboration with him to study four and now seven ringed aromatic molecules as well.

Primarily, what you'll see in presentations from my group are new spectra presented on different molecules from our instruments or working in collaboration with Mike, and then the detections of some of those molecules in space, or in many cases, the non-detections, because most often you don't detect the molecule you are looking for. Then, talks on the interpretation of those in terms of what we're learning about the chemistries of these sources, and talks about the tools and techniques of spectroscopy and machine learning that we're bringing to bear on the problem.

References

1. Massachusetts Institute of Technology, Brett McGuire. MIT.edu. Available at: https://chemistry.mit.edu/profile/brett-mcguire/ (accessed 2025-06-20).
2. Wetzel, W. Previewing the 78th International Symposium on Molecular Spectroscopy. Spectroscopy. Available at: https://www.spectroscopyonline.com/view/previewing-the-78th-international-symposium-on-molecular-spectroscopy (accessed 2025-06-20).