Rotational Spectroscopy of Molecular Complexes

Rotational spectroscopy exploits the absorption or emission of electromagnetic radiation by molecules as they undergo transitions between quantised rotational energy levels. When applied to molecular complexes—non-covalent assemblies formed via hydrogen bonding, halogen bonding, metal–ligand interactions or tetrel bonds—it provides precise measures of structural parameters, intermolecular forces and dynamics. By analysing rotational constants and associated distortion parameters, researchers determine bond lengths, angles and force constants, thereby elucidating the geometry and strength of the interaction within the complex. Supersonic expansion of a gas mixture often cools molecules to their rotational ground states, simplifying spectra and enhancing resolution. Techniques such as chirped-pulse Fourier transform microwave spectroscopy permit rapid, broadband acquisition of spectral lines, enabling the characterisation of multiple isotopologues and revealing subtle variations arising from isotopic substitution or ligand identity. Recent advances include coupling of rotational spectroscopy with laser ablation sources to generate transient metal-containing complexes and the integration of rotational measurements with high-level ab initio calculations to benchmark non-covalent interaction models. Together, these approaches have deepened our understanding of weak intermolecular forces that underlie phenomena ranging from atmospheric chemistry to catalysis and materials assembly.

Research from Nature Portfolio

No recent Nature Portfolio content available.

Rotational Spectroscopy of Molecular Complexes publication trend

The graph below shows the total number of articles in rotational spectroscopy of molecular complexes across all publications each year (not limited to Nature Index journals).

Technical terms

Rotational spectroscopy: A method that measures transitions between quantised rotational levels of molecules to infer structural and dynamical properties.

Chirped-pulse Fourier transform microwave spectrometer: An instrument that emits a sweeping microwave pulse and captures free induction decay, enabling rapid, broadband acquisition of high-resolution rotational spectra.

Rotational constant (B₀): A parameter inversely proportional to the moment of inertia of a molecule, used to determine bond lengths and molecular geometry.

Centrifugal distortion constants (D_J, D_JK): Corrections to the rigid-rotor model accounting for bond stretching at higher rotational excitation.

Nuclear quadrupole coupling constant (χ_aa): A parameter describing the interaction between a nucleus with spin greater than ½ and the electric field gradient, providing information on electronic environment and molecular symmetry.

References

1. A perspective on chemistry in transient plasma from broadband rotational spectroscopy. Physical Chemistry Chemical Physics (2014).
2. Gas phase complexes of H 3 N⋯CuF and H 3 N⋯CuI studied by rotational spectroscopy and ab initio calculations: the effect of X (X = F, Cl, Br, I) in OC⋯CuX and H 3 N⋯CuX. Physical Chemistry Chemical Physics (2016).
3. H 3 P⋯AgI: generation by laser-ablation and characterization by rotational spectroscopy and ab initio calculations. Physical Chemistry Chemical Physics (2016).