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Twins in rotational spectroscopy: Does a rotational spectrum uniquely identify a molecule?
Marcus Schwarting1, Nathan A Seifert2, Michael J Davis3
1Department of Computer Science, University of Chicago, Chicago, Illinois 60637, USA.
The Journal of Chemical Physics
|July 25, 2024
Summary
Molecular twins, molecules with similar rotational spectra but different structures, exist. This challenges the uniqueness of rotational spectroscopy fingerprints, suggesting the inverse problem is ill-posed.
Area of Science:
- Physical Chemistry
- Spectroscopy
- Computational Chemistry
Background:
- Rotational spectroscopy is a precise technique for gas-phase molecular structure determination.
- It is widely assumed that a molecule's rotational spectrum serves as a unique identifier.
- Advancements in molecular databases and AI necessitate re-evaluating this assumption.
Purpose of the Study:
- To investigate if distinct molecules can exhibit similar rotational spectra.
- To frame molecular structure determination from rotational spectra as an inverse problem.
- To identify 'molecular twins' with similar spectra but different structures.
Main Methods:
- Formulated molecular structure determination as an inverse problem.
- Employed a funnel-based search strategy to identify molecular twins.
- Generated rotational constants for numerous molecules using computational methods and large databases.
Main Results:
- Demonstrated the existence of molecular twins within typical computational accuracy.
- Indicated that the inverse problem of determining molecular structure from rotational spectra is ill-posed.
- Showcased that some molecular twins can be differentiated with higher accuracy methods or additional experiments.
Conclusions:
- The assumption of unique rotational spectra fingerprints is challenged.
- The inverse problem is ill-posed, meaning a unique solution may not always exist.
- Higher accuracy computations and experimental data can help resolve ambiguities for some molecular twins.
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