Investigación

Defining Molecular Structure with CP-FTMW Spectroscopy

A New Frontier at the Intersection of Physical Chemistry and Structural Physics

Our laboratory develops advanced Chirped-Pulse Fourier Transform Microwave (CP-FTMW) spectrometers, pushing the boundaries of molecular detection and characterization. Unlike traditional methods that merely identify molecular presence, our approach defines the precise three-dimensional coordinates of molecules and molecular aggregates, offering unparalleled insight into their spatial arrangement.

Capturing Rotational Signatures for Structural Determination

By measuring the distinct rotational frequencies of gas-phase species, we unlock an absolute structural "fingerprint". This capability transforms our understanding of molecular architecture, providing a level of detail that is essential for a wide range of scientific areas such as pharmaceutical development and the study of life's origins in the cosmos. By delivering precise molecular coordinates, our work lays the foundation for future discoveries and innovations in both chemistry and physics.

Our work is based on the quantization of rotational kinetic energy. A molecule's energy levels are defined by its Principal Moments of Inertia (Ia, Ib, Ic). Because these moments are derived from the mass distribution relative to the center of mass, any change—the rotation of a hydroxyl group, the addition of a water molecule, or a change in atomic mass—shifts the spectrum. We use these small changes in the spectrum to derive accurate structural information.

Historically, microwave spectroscopy was a "narrowcast" technique. Our lab utilizes Broadband CP-FTMW, which functions similarly to modern NMR:

Arbitrary Waveform Generation: We create a "chirp"—a rapid frequency sweep that polarizes the entire sample near-instantaneously.
The FID Response: We record the Free Induction Decay, the coherent electromagnetic "echo" emitted by the rotating molecules as they relax.
Fourier Analysis: We transform this time-domain data into a high-resolution frequency map, allowing us to identify dozens of different chemical species simultaneously in a single measurement.

Research Pillar I: Water Clusters & Microsolvation

Water is the universal solvent, yet its behavior at the molecular level remains one of science's greatest mysteries. We bridge the gap between single molecules and bulk liquid by studying discrete water clusters.

Hydrogen-Bonding Networks: We map the precise geometry of (H₂O)ₙ clusters to understand how water organizes itself through non-covalent interactions.
Step-wise Microsolvation: By adding water molecules one-by-one to a host molecule, we observe how the "solvent shell" alters the host’s structure and chemical reactivity.
Proton Dynamics: Our high-resolution spectra allow us to observe quantum mechanical tunneling, where water molecules "flip" or "rearrange" within a cluster, providing a window into the fundamental motion of hydrogen bonds.

Links

Concerted hydrogen-bond breaking by quantum tunneling in the water hexamer prism | Science(link is external)

Rotational dive into the water clusters on a simple sugar substrate | PNAS(link is external)

Water Cooperativity Impacts Aromatic Interactions in the Aggregation of Benzene with Water | Journal of the American Chemical Society(link is external)

Hydrogen Bond Interaction Networks in the Mixed Pentamers of Hydrogen Sulfide and Water | Journal of the American Chemical Society(link is external)

Research Pillar II: Chiral Sensitive Techniques

Chirality—the "handedness" of molecules—is critical in drug design, where one enantiomer may heal while its mirror image is inert or toxic. We have contributed to developing methods to perform chiral analysis without separation.

Chiral Tagging: By introducing an enantiopure "tag" molecule, we create clusters that turn enantiomers into diastereomers. These have different moments of inertia and appear as distinct, quantifiable peaks in our spectrum.
Microwave Three-wave Mixing: We combine experimental data with Computational Quantum Chemistry to determine the 3D orientation of a molecule with 100% certainty and determine the enantiomeric excess, bypassing the need for X-ray crystallography, GC or pure samples.
Enantiomer-selective Population Transfer: We use sophisticated pulse sequences to selective populate a rotational level of choice with the desired enantiomer. This sets the stage for future experiments that will enable chiral separation by optical means.

Links

Coherent Enantiomer‐Selective Population Enrichment Using Tailored Microwave Fields - Pérez - 2017 - Angewandte Chemie International Edition - Wiley Online Library(link is external)

State-Specific Enrichment of Chiral Conformers with Microwave Spectroscopy | The Journal of Physical Chemistry Letters(link is external)

Research Pillar III: Astrochemistry & The ISM

The space between stars is a vast chemical laboratory. We use our spectrometers to provide the "gold standard" data required to identify new molecules in the Interstellar Medium (ISM). This entails collaborations with synthetic chemistry labs and telescope observational groups.

Laboratory Astrophysics: Using pulsed-jet expansions and buffer-gas cooling techniques, we reach temperatures as low as 2 K, mimicking the freezing conditions of molecular clouds.
Prebiotic Chemistry: We search for building blocks of life and PAH, providing the spectral "fingerprints" used by telescopes.
Exotic Species: We generate and characterize reactive species, radicals and ions that are unstable on Earth but thrive in the vacuum of space.

Links

Discovery of interstellar phenalene (c-C13H10): A new piece in the chemical puzzle of PAHs in space | Astronomy & Astrophysics (A&A)(link is external)

Discovery of two new isomers of cyanoacenaphthylene (C12H7CN) in the Taurus molecular cloud 1 with the QUIJOTE line survey | Astronomy & Astrophysics (A&A)(link is external)

Discovery of two cyano derivatives of acenaphthylene (C12H8) in TMC-1 with the QUIJOTE line survey | Astronomy & Astrophysics (A&A)