An interactive molecular simulation of the normal modes of vibration and the associated infrared and Raman spectra of small molecules is presented. The user is presented with an intuitive interface permitting the selection of any desired normal mode and a slider for selection of the speed of the presented motion.
Type of Material:
This applet is a molecular simulation/animation of normal vibrational modes.
This software is intended for visualization of the vibrational process of molecules. Every discussion of the principles of IR and Raman spectroscopy and normal mode analysis/use would greatly benefit from the use of this web site.
The site is geared to providing a visual demonstration of normal modes of vibration for small molecules, showing clearly the distinction between Raman and IR activity.
Target Student Population:
This animation is targeted at undergraduate students, who are studying either IR spectroscopy or Raman spectroscopy.
Prerequisite Knowledge or Skills:
Students need to be studying the theme of normal modes, otherwise they will not grasp the full ramifications of Raman vs. IR activity etc. Students should have been introduced to the concept of Raman and IR selection rules.
Users are able to select from a substantial list of small molecules, observe the IR and Raman spectra and select the particular normal modes of interest, studying from any aspect the nature of the motion for the particular mode at a selectable speed.
The spectra should have a few more grid markers indicating spectral position.
Potential Effectiveness as a Teaching Tool
1. The large number of structures in the database allow for a large number of representative vibrational modes to be visualized.
2. This site is perfect for showing normal vibrational modes, their Raman and IR activity, and the position in the spectra. No discussion of Raman and IR spectroscopy is sufficient if it does not include the explicit demonstration and use of this web site.
1. The molecules in the database remain relatively small (i.e., a small number of atoms), presumably because of the high level calculations used to produce the vibrational frequencies.
2. No background information or learning materials are associated with this animation program.
3. The spectral lines need to be a little bit thicker so that they are more easily observed on higher resolution monitors (especially the highlighted mode).
4. It would be helpful if those examples which are IR and not Raman or vice versa (at least to first order) were complemented by some sort of visualization associated with dipole moment change etc. This may be asking a lot but would help the users understand WHY some modes are active one way and not the other.
Ease of Use for Both Students and Faculty
The web site comes up quickly and the operation of the controls on the interactive applet is intuitive and simple. This, along with the companion site, MOLSYM, set a new gold standard for excellence in interactive web sites, at least in spectroscopy, physical chemistry, and symmetry discussions.
When a particular mode is selected for study, the appropriate simplified spectral line is displayed in blue. However, the lines are so narrow that it is hard to resolve the color difference between dark blue and black. It would be better to make the simplified spectral lines perhaps 2 pixels wide and choose a color with higher contrast. It is also difficult to mouse over the C-H stretch lines and get them to show up with the tool tips mouse indicator.
Other Issues and Comments:
Future revisions might include a set of questions to help students explore the relative vibrational modes. This would help students to learn about the differences between stretching modes, bending modes, or rotational modes. This might also allow students to see the differences between the effects of mass on a vibrational mode or even why a mode is Raman active vs IR active. However, any serious discussion of Raman and IR activity is not complete without demonstration and use of this web site. Every aspect is covered by the interactive applet.
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