Molecular Spectroscopy and Structure

Rotational spectroscopy probes how molecules spin in the gas phase, and because each molecule's rotational energy levels form a unique fingerprint, the technique can determine bond lengths, bond angles, and three-dimensional geometry with exceptional precision. Modern approaches — particularly chirped-pulse excitation and Fourier transform microwave methods — have made it possible to capture broadband spectra of complex molecules in milliseconds, revealing subtle features like hydrogen bond geometries, the coexistence of multiple conformers, and the dynamics of internal rotation. Isolating molecules in the gas phase removes the complicating influence of solvents and crystal packing forces, giving a cleaner view of intrinsic molecular behavior. Active questions in the area include understanding how conformational preferences shift when weak interactions such as C–H···O hydrogen bonds compete with steric effects, and how torsional tunneling between nearly equivalent structures influences the observed spectrum.

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58,132

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Keywords

Rotational SpectroscopyMolecular StructureBroadband Microwave SpectroscopyGas PhaseHydrogen BondsConformational Dynamics