ATR-IR spectroscopy

Attenuated total reflection infrared (ATR-IR) spectroscopy is one of the few available tools to investigate processes taking place at solid-liquid interfaces.

The technique was developped by N. Harrick in the 60's and is based on the propagation of the infrared radiation through a material (internal reflection elecment, IRE) of high refractive index (n_IRE) and its reflection at the interface between the IRE and the medium in contact with it (medium 2, refractive index n₂). Two conditions must be satisfied in order to observe internal total reflection, i) that the angle of incidence of the infrared radiation is larger than the critical angle of the IRE (characteristic for each material), and ii) that n_IRE>n₂. Then the theory predicts that the infrared radiation penetrates into medium 2, that an evanescent electromagnetic wave is generated at the interface and that the radiation propagates through te IRE upon successive internal reflections.
The extent of penetration of the radiation into medium 2 practically depends on the wavelength and on the optical properties (refactive indices and angle of incidence) of the sample (IRE+medium 2). For example, it will be about 0.9 microns at 1700 cm^-1 for a ketone in contact with ZnSe (n_IRE= 2.4).

The example reveals how ATR-IR spectroscopy can be highly surface sensitive, if a thin film of a solid material is set at the IRE-liquid interface. The sensitivity can be in principle adjusted by selecting the appropriate IRE material and medium 2.

This last observation is the motivation of the use of ATR-IR spectroscopy to understand processes occurring at solid-liquid interfaces at a molecular level.
Here, the solid-liquid interface is intended as the interface generated by the contact of a thin film of a solid material deposited onto the IRE and a solution.

Such interfaces are relevant in a number of research fields.
At present, we carry out studies in heterogeneous catalysis and separation science, which involve studies of reaction and adsorption on powder materials and model thin films.

Read some reviews

''Attenuated total reflection infrared spectroscopy of solid catalysts funtioning in the presence of liquid-phase reactants''
T. Bürgi, and A. Baiker, Adv. Catal. 50 2006 227
''Sensor applications of attenuated total reflection infrared spectroscopy''
C. Vigano, J.-M. Ruysschaert, and E. Goormaghtigh, Talanta 65 2005 1132
''In situ Fourier-transform infrared spectroscopy studies of inorganic ions adsorption on metal oxides and hydroxides''
G. Lefèvre, Adv. Colloid Interface Sci. 107 2004 109
''Probing solid/solution interfacial chemistry with ATR-IR spectroscopy''
A.J. McQuillan, Adv. Mater. 13 2001 1034
''At the solid/liquid interface: FTIR/ATR - the tool of choice''
A.R. Hind, S.K. Bhargava, and A. McKinnon, Adv. Colloid Interface Sci. 93 2001 91
''New directions and challenges in modern electrochemistry: in situ infrared spectroscopy of the semiconductor/electrolyte interface''
J.-N. Chazalviel, B.H. Erné, F. Maroun, and F. Ozanam, J. Electronal. Chem. 502 2001 180