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Accueil > EN > Research Areas > Pure and applied spectroscopy > Microwave and (sub)millimeter-wave spectroscopy > Molecular structures


par Manuel GOUBET - publié le , mis à jour le

The major characteristic of a molecular system is undoubtedly its structure. Most of the macroscopic properties come therefrom. For example, the knowledge of the structure is fundamental to biological molecules which can deform, fold, unfold, to adapt themselves to a potential receiver for a recognition as selective as possible ; it is the key parameter to its biological functionality.

In this realm, molecular spectroscopy is the method of choice. Indeed, recording and modelling of the spectrum of the molecule, which is its fingerprint, can lead to experimental identification of its structure (see figure below, left panel). It is particularly the case of microwave spectroscopy : direct observation of the rotation of a molecular system around its inertial axes provides its moments of inertia, which correspond to one unique geometry (see figure below, right panel).

Spectrum = fingerprint
Spectrum = fingerprint
Infrared spectra of 3 isomers of the dimethylbenzaldehyde. Spectra are very differents only because of the change of position of the CH3 groups around the aromatic ring.
Pure rotational spectra
Pure rotational spectra
Microwave spectra of 2 conformers of urethane. The slight change in geometry (torsion of the C—O bond) results in a shift of the rotational lines of about 1 GHz.