Connections between the accuracy of rotational constants and equilibrium molecular structures

Rotational spectroscopy is the technique of choice for investigating molecular structures in the gas phase. Indeed, rotational constants are strongly connected to the geometry of the molecular system under consideration. Therefore, they are powerful tools for assessing the accuracy that quantum chemical approaches can reach in structural determinations. In this review article, it is shown how it is possible to measure the accuracy of a computed equilibrium geometry based on the comparison of rotational constants. But, it is also addressed what accuracy is required by computations for providing molecular structures and thus rotational constants that are useful to experiment. Quantum chemical methodologies for obtaining the 0.1% accuracy for rotational constants are reviewed for systems ranging in size from small molecules to small polycyclic aromatic hydrocarbons. This accuracy for systems containing two dozen or so atoms opens the way towards future applications such as the accurate characterization of non-covalent interactions, which play a key role in several biological and technological processes.

Automated summary

Rotational spectroscopy is the preferred technique for studying molecular structures in the gas phase. Rotational constants are strongly linked to the geometry of the molecules, making them useful for evaluating the accuracy of quantum chemical approaches. This review article discusses how the accuracy of computed equilibrium geometry can be measured by comparing rotational constants, and also explores the required accuracy for providing useful molecular structures and rotational constants. Quantum chemical methodologies for achieving 0.1% accuracy in rotational constants are reviewed, ranging from small molecules to small polycyclic aromatic hydrocarbons. This level of accuracy opens up possibilities for future applications, such as accurately characterizing non-covalent interactions in biological and technological processes.