Part 1: Boron Based Acids

F: Animating the Vibrations

Now we are ready to look at the output from the frequency, or vibrational analysis. We will be animating the vibrations and looking at the computed IR spectrum.

  • Animating the vibrational frequencies
    • if you didn't open the frequency job when if finished, do so now
    • From the main menu along the top of the screen (in gaussview) choose "Results" and then choose "Vibrations":

    • a new window will open called "Display Vibrations":

    • arrange your windows so that you can see both the molecule window and the vibration window
    • in the molecule window rotate your molecule so it is not completely in the plane of the screen
    • in the vibration window highlight the top vibration, then check the "Show Displacement Vectors" box, and finally click on the "Start" button, the molecule should start vibrating!
    • look at all the vibrations by highlighting them one after another down the list
    • If you have any vibrations with a negative number under the frequency heading this means your molecule is not fully optimized, go back repeat the frequency analysis making sure that you take the log file from the optimization. If that doesn't work repeat your optimization, and then frequency analysis. If you are still unsuccessful get a demonstrator to help you determine what is wrong.
    • you should have 6 vibrations, with frequencies similar (but not necessarily identical) to my example
    • the number in the IR column identifies the intensity of each vibration
    • For your presentation make up a table that summarises the form, frequency and intensity of each vibration for trigonal planar BH3. Use your knowledge of the point group of BH3 to determine the symmetry label for each vibration.
  • The IR spectrum
    • in the vibration window click on the button "spectrum", and enlarge the window that opens, this is the computed IR spectrum for your molecule
    • use a "window capture" application to take a snap-shot of the spectrum and include it in your presentation. In your presentation explain why are there less than six peaks in the spectrum?
  • When you are ready close the molecule window move onto the next step
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