Frequency Calculations
- all molecules vibrate
- vibrations occur at specific frequencies, depending on the molecule/ functional group
- measurement of he frequencies of a molecule allows chemists to identify the molecule by a spectra, such as an infrared (IR) specra
- molecules have a specific number and type of vibrations, depending on "N", the number of atoms
- number: 3*N-6 for nonlinear molecules, 3*N-5 for linear molecules
Even when we are concerned about the motion of the nuclei, we do not include all possible factors on that motion in the model. Since we do not account for the electron interactions caused by the vibrations of the nuclei, the frequencies that are calculated are almost always larger than the observed frequencies, by as much as 15%. Usually, calculated frequencies are "scaled", that is, reduced to 85% of the calculated value to give a better approximation of the actual values.
[Previous][Next]
[CompChem Main Page][Contents]
[1]
[2]
[3]
[4]
[5]
[6]
[7]
[8]
[9]
[10]
[11]
[12]
[13]
[14]
[15]
[16]
[17]
[18]
[19]
[20]
[21]
[22]
[23]
[24]
[25]
[26]
[27]
[28]
[29]
[30]
[31]
[32]
[33]
[34]
Developed by
The Shodor
Education Foundation, Inc.
Copyright © 1998
Last Modified:
Questions or comments about this page should be directed to gotwals@shodor.org