Welcome to the Gru Lab at Tennessee Tech University!

The Gurusinghe Research Lab at Tennessee Tech University, “Gru Lab”, studies molecular spectroscopy and reaction dynamics/kinetics using various Fourier transform microwave and millimeterwave (FTMW and FTmmW) spectroscopic and resonance-enhanced ionization techniques.

The Instrument: L-Shaped Fourier transform microwave (L-FTMW) spectrometer

Our lab’s newest custom-built rotational spectrometer features a novel L-shaped configuration that uniquely combines cavity-enhanced and chirped-pulse Fourier-transform microwave (FTMW) spectroscopy in a single instrument. This innovative geometry offers a low-cost and straightforward design for integrating these two complementary techniques, while also simplifying integration with external photolysis lasers.

The cavity-enhanced microwave setup employs a Fabry–Perot resonator to boost sensitivity and achieve high spectral resolution (~ 2.5 kHz) making it ideal for resolving subtle hyperfine splittings and extracting detailed molecular information. In parallel, the chirped-pulse microwave setup provides rapid, broadband spectral coverage, enabling efficient surveys of complex mixtures and time-dependent tracking of multiple species simultaneously. The chirped-pulse system’s broadband horn antennas are mounted externally on a microwave-transparent polycarbonate chamber, allowing flexible repositioning along the molecular beam path. A multi-antenna mount also allows seamless switching between different frequency bands, greatly improving efficiency in broadband data collection.

Together, this integrated dual-technique platform opens new possibilities for addressing fundamental chemical questions and probing astrochemically relevant molecules with both precision and speed.

Our latest research: Near-free rotor limit quantum tunnelling in 3-methylstyrene conformations

Our latest study presents the first high-resolution rotational spectra of both cis and trans conformers of 3-methylstyrene, a molecule exhibiting near free-rotor methyl torsion. Using jet-cooled FTMW spectroscopy, we precisely measured quantum tunneling splittings arising from extremely low torsional barriers. These splittings were rigorously analyzed and fitted using multiple torsion-rotation Hamiltonians (XIAM and BELGI-Cs), enabling detailed characterization of methyl internal rotation and conformer-dependent dynamics.

Beyond torsional analysis, the work makes a valuable contribution to the long-debated question of structural planarity in styrene derivatives. By deriving second moments from experimentally determined rotational constants, we provided strong evidence for planar heavy-atom geometries in both conformers, despite minimal energy differences and competing steric effects.

This research was featured in the Journal of Chemical Physics Emerging Investigators Special Collection and selected for the cover of the January 2025 issue.