Spectroscopic Simulator Info

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A simulation of the vibrational/rotational spectrum of a diatomic molecule (for physical chemistry courses).

This simulation of an infra-red spectrometer allows students to adjust the experimental and molecular parameters and observe the effects on the infra-red spectrum.

It covers an aspect of the Physical Chemistry II course that students often find confusing. Although it is based on relatively simple mathematics, a complete understanding of the phenomenon requires assimilating the following concepts:

  • The energy levels of a diatomic molecule are given by the formula: E(v,J) = hv (v + ½) + BJ (J + 1); v = 0..infinity, J=0..infinity
  • A molecule absorbs light at frequencies that correspond to difference between energy levels. In this case, we are interested in the following differences, frequency of light: E (v = 1, J') - E (v = 0, J); with J' = J + 1 or J -1
  • The intensity of the transition is proportional to the population of the lower state, intensity is proportional to: (2J + 1) exp[-E (v = 0, J) / kT]

Many students are comfortable with these separate concepts, but find it difficult to combine them together to produce an understanding of rovibrational spectroscopy. Students may use the applet to first focus on each of the individual concepts, within the context of the actual experiment, and then to integrate these concepts into a coherent whole.