Facilities: Optical Spectroscopy Instrumentation

Infrared Spectroscopy

The amount of energy a molecule contains is not continuously variable but quantized. This means that a molecule can stretch, bend, or rotate only at specific frequencies. For example, a typical C-H bond has an average bond length of 1.10 Angstroms. This length is only an average – vibrating back and forth due to stretching, bending, and rotation (both symmetrically and asymmetrically) are all happening on a moment by moment basis.

When the molecule is irradiated with electromagnetic radiation, the vibrating bond will absorb energy if the frequencies of the light and the vibration are the same. This absorption phenomena is the principle the IR takes advantage of in the production of spectra that can be easily interpreted by the trained chemist.

The above graph, of an unknown sample, shows specific regions where the vibrations are characterized. The IR is a popular tool used by inorganic, organic, and physical chemists due to the variety of information it conveys in a fast amount of time.

Nicolet iS5 FTIR (2015)

Nicolet 380 FTIR (2006)

Contact Information:

Dr. Michael Norton
Dept. of Chemistry

Email: norton@marshall.edu

Phone: 304-696-3489

Dr. Gary Anderson
Dept. of Chemistry

Email: anderson@marshall.edu

Phone: 304-696-6594

Dr. Michael Castellani
Dept. of Chemistry

Email: castella@marshall.edu

Phone: 304-696-6486

Nicolet iS50 FTIR with Smart Diffuse Reflectance (2014)

Contact Information:

Dr. Rosalynn Quinones
Dept. of Chemistry

Email: quinonesr@marshall.edu

Phone: 304-696-6731

Matrix Isolation FTIR: Bruker FTIR with pyrolysis unit and cryostat cell (2009)

Contact Information:

Dr. Laura McCunn
Dept. of Chemistry

Email: mccunn@marshall.edu

Phone: 304-696-2319

Bruker Optics Vertex 70 FTIR Spectrometer (2008)

Contact Information:

Dr. Laura McCunn
Dept. of Chemistry

Email: mccunn@marshall.edu

Phone: 304-696-2319

UV/Vis Spectroscopy

Ultraviolet spectroscopy is applicable solely to conjugated systems. This is because most organic compounds produce no effect whenever the relatively high-energy radiation that constitutes the ultraviolet (200–400 nm) and visible (400–700 nm) portion of the electromagnetic spectrum are presented. Whenever ultraviolet radiation is used, the energy absorbed by a molecule corresponds to the amount necessary to excite electrons from one molecular orbital to another. Typical organic compounds, which mostly contain s bonds, require much higher wavelengths to become excited than what the range of UV will provide. Only those conjugated systems with a number of p bonds are capable of being promoted to higher energy levels by ultraviolet and visible light.

A sample is placed into a cuvette and the spectrum is recorded by irradiating the sample with ultraviolet light of continuously changing wavelength. When the wavelength of light corresponds to the energy level required to excite an electron to a higher energy level, energy is absorbed. This absorption is detected and plotted on the vertical axis as the absorption while the wavelength of the absorbed light is plotted horizontally.