Infrared Spectroscopy

Part of the Industrial Science Project

Goal

When the Canadian Light Source (CLS) opens in Saskatoon in 2004, there will be 2 infrared (IR) beamlines: a high resolution far-IR beamline and a mid-IR microspectroscopy beamline. The Alberta Synchrotron Institute mission with respect to the IR project is to promote usage of synchrotron-based IR radiation and to assist in the training of those Alberta-based industrial and academic scientists who will use it.

IR Radiation and Spectral Information

Infrared radiation is the electromagnetic radiation that is between the visible red and microwaves. It is usually divided into 3 subranges: Near-IR (roughly 13,000 - 4000 cm^-1), mid-IR (4000 - 400 cm^-1) and far-IR (400 - roughly 10 cm^-1). The IR region corresponds to the frequencies of vibrations of atoms within molecules.

The information contained in an infrared spectrum of a sample is present in three principal forms: the frequencies, the intensities, and the bandshapes of the vibrations. Analysis of these forms can lead to a wealth of knowledge about the molecular state of the sample.

Of the three forms, the vibration frequency information is the one mostly used, as it is by far the easiest to obtain and also because it provides qualitative information about the nature of the atoms in the sample involved in the vibration. This is due to the fact that vibration frequencies depend on the mode of vibration (e.g. stretch, bend, symmetric, etc.) and the type of atoms involved. In the infrared region, vibrations are often reported not using the frequency (cycles per time unit) but rather using wavenumbers (cm^-1 = wavenumber = reciprocal of a cm) which is directly proportional to the frequency through the speed of light in vacuum. Thus, it is often possible to correlate an observed wavenumber with tabulate wavenumbers of typical vibrations and determine the possible nature of the vibration.

The intensity of a vibration is related to the relative response of the electron density of individual bonds associated with the vibrational motion. In principle the intensity can provide both qualitative and quantitative information that can be used in theoretical studies as well as in analytical studies for the determination of concentrations.

Intensities are often measured as the peak height of a feature in the spectrum relative to the level of noise in the baseline near it. The greater this signal-to-noise ratio (S/N) is, the more accurate is the intensity measurement and consequently its interpretation. This means that intensity information is highly sensitive to the quality of the sample, the state and capabilities of the instrument, and the measurement technique. It also means that great experimental efforts are constantly made to improve the S/N ratio and thus improve detection limits.

The Synchrotron Advantage

Suppose that the desired infrared spectrum is that of a very small sample, either because it is physically very small or due to low concentration. To achieve a reasonable S/N ratio, either a "concentration" of the sample or of the infrared beam is needed. If modification of the sample is impossible or undesired, then the only possible improvement is in the infrared beam.

A synchrotron source produces light that is about 1000 times brighter than that of a conventional source (e.g. globar). In addition, and unlike globar, the synchrotron infrared light is highly collimated like a laser and yet is emitting in all the infrared wavelength range. This means that the synchrotron infrared beam is highly efficient to focus on a small spot.

Hence, it is possible to use an IR microscope coupled to a synchrotron source, allowing one to investigate sample sizes down to the physical limit (diffraction limit of the incident radiation is 5-20 microns depending on the wavenumber), obtain a scan about 30 times faster than with a conventional globar source and still get a spectrum with a very good S/N ratio.

Applications of Synchrotron-based Infrared Microspectroscopy

Because of the synchrotron-based infrared capabilities it is possible to obtain detailed information for a wide range of systems. Listed below are just a few references and links (when available) to synchrotron-based studies.

• Biological Systems

Gough, K. et al., "Synchrotron infrared microspectroscopy of cardiomyopathic heart tissue" (pdf file)

Jeruzalmi, D. et al., "Structure and mechanism of the DNA polymerase processivity clamp loader" (pdf file)

Juurlink, B. et al., "FTIR evaluation of mouse tissue preparation procedures" (pdf file)

Wetzel, D.L. and Williams, G.P. "Localized (5 mm) probing and detailed mapping of hair with synchrotron powered FT-IR microspectroscopy", in Fourier Transform Spectroscopy, J.A. de Haseth (ed.) 302-5 (1998).

• Materials Sciences

Eng, C.W. et al., "Using synchrotron FTIR microspectroscopy to study the interaction between uranium and atmospheric corrosion products on steel" (pdf file)

Srinivasamurthi, V. et al., "Corrosion studies of aluminum, iron and other metals using grazing angle infrared micro-spectroscopy" (pdf file)

Vasquez, M.J. et al., "Heterogeneity in chromate conversion coatings (CCC) on Al-Cu alloy AA2024-T3 used for aerospace applications" (pdf file)

Wetzel, and Carter III, R.O. "Synchrotron powered FT-IR microspectroscopic incremental probing of photochemically degraded polymer films", in Fourier Transform Spectroscopy, J.A. de Haseth (ed.) 567-570 (1998).

• Geological and Environmental Sciences

Seaman, S. et al., "Crystal/melt distribution of water during crystallization of felsic magma" (pdf file)

Song, Z. et al., "FTIR investigations of sediments from NY/NJ harbor, San Diego bay, and the Venetian lagoon" (pdf file)

• Plant Sciences

Wetzel, D.L. et al., "Ultraspatially-resolved synchrotron infrared microspectroscopy of plant tissue in situ", Cell. Mol. Biol., 44 (1), 145-167 (1998).

Wetzel,D.L., "Analysis of individual protein bodies in situ in wheat endosperm with infrared synchrotron microspectroscopy" (pdf file)

Participating Research Team (PRT) with U10B at NSLS

The Canadian Light Source (CLS) has become a partner in an IR microspectroscopy beamline at the National Synchrotron Light Source (NSLS) in Brookhaven National Laboratory in New York (beamline U10B). This arrangement allows the CLS to offer time to Canadian researchers who are interested in pursuing synchrotron based IR studies. In fact, 25% of the beamline time is allocated to CLS users. This agreement provides a great opportunity for Canadian researchers to train, gain expertise and run experiments prior and in anticipation of the opening of CLS.

The Alberta Synchrotron Institute has taken advantage of this arrangement and its staff went last year on 3 trips to Brookhaven and collected data on behalf of Alberta researchers. On the last trip, Dr. H. Wieser of the University of Calgary and one of his students explored the feasibility of interfacing vibrational circular dichroism (VCD) to a synchrotron IR source.

To view the specifications of U10B click here. In addition to U10B there are several other infrared beamlines in NSLS. Although the CLS doesn't have a PRT agreement, it is possible to obtain time on these beamlines through a general user allocation by submitting a research proposal. ASI can provide assistance and contact references with these proposals, and can also provide financial assistance for the travel costs. For more information, please contact .