What is Infrared Vibrational Spectroscopy?
IR spectroscopy provides the structural information (think functional groups) of molecules by measuring the absorbance of infrared energy in the vibrational movement of the bonds within a molecule.
Why do we use IR spectroscopy?
- Excited molecular vibrations provide information on functional groups.
- Information about peak positions, intensities, widths, and shapes are unique.
- For characterization of new compounds.
Instructions for using the IR:
- Open the “Omnic” software (not “Omnic spectra”).
- Open the Experimental Setup window (top left of the screen, “Expt Set”) and make sure the instrument has the following parameters: 16 scans (to save time) and collect background before every sample (everything else is fine as-is). Click OK to close the window.
- Make sure that the sample platform and the anvil (the metal cylinder that crushes the sample over the window) are clean. If they are not, wet a kimwipe with methanol from a bottle on the table next to the instrument, wipe off the stage and the anvil, and dry so no residual solvent remains to interfere with the IR signal.
- Click the “Col Smp” icon to begin the collection process (top left corner) and enter a name for the spectrum when prompted, and click “OK.” A new prompt will appear instructing you to prepare for the background signal collection.
- Screw down the anvil onto the sample stage (over the glass window of the light source) until it is touching, then further tighten until the knob clicks one time. Click “OK” on the Background Confirmation text box to begin collecting the background sample.
- After the background is finished, a new prompt will appear and tell you to prepare to collect the sample spectrum. Loosen the anvil to remove it from the sample window, place a small amount of your sample onto the window (just enough to cover the glass), and re-tighten the anvil, crushing the sample. Click “OK” to begin sample spectrum acquisition.
- After the instrument finishes collecting the spectra, a new prompt appears. Click “Yes” under the question “Add to Window 1?”
- You may now save your spectrum by either clicking the save icon (top left) or going to the “File” > “Save As” option in the toolbar. Save as a “.CSV” (comma separated value) file type if you intend to plot this in excel. Email the data, add to a USB, or upload to cloud storage.
- Once the data is saved, exit the program and CLEAN THE SAMPLE STAGE + ANVIL!!!
Reporting your IR Spectra:
- Plot your data. The x-axis should be 3900-750 cm-1 from left to right.
- Include the structure of your compound (use ChemDraw).
- Include a table of bonds, peak frequency (in cm-1) and intensities.