Raman scattering

[basophilic]

In a Raman scattering event, the photon’s:

A. frequency will increase and its wavelength will increase.
B. frequency will increase and its wavelength will decrease.
C. frequency will decrease and its wavelength will increase.
D. frequency will decrease and its wavelength will decrease.

Passage states Raman scattering is INELASTIC, which is true. However, from chemistry class I remember that Raman scattering could involve EITHER a loss (Stokes scattering) OR gain (anti-Stokes) in energy; energy loss is straightforward in that a ground vibrational/ground electronic state is excited to a virtual electronic state and then relaxes down to ground electronic but EXCITED vibrational state. However, energy gain results from electrons going from ground electronic/EXCITED vibrational to a virtual electronic state back down to ground electronic/GROUND vibrational state. Hence, frequency should be able to increase OR decrease (TPR's answer is C). Granted that the anti-Stokes scattering is less probable, but probability is not really taken into account at least from the question stem. Is this an ambiguous question, then?

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[MrRed]

You're definitely correct in stating that Raman scattering can be either Stokes or Anti-Stokes, and thus the photon can either be a lower or higher energy than originally absorbed by the atom, however if the passage only states that the collision is inelastic; then the best answer is C.
In inelastic collision, as you know, kinetic energy is not conserved.

In this case -- I believe -- they are using an overly complicated model simply to sneakily convey an elementary physics scenario -- they don't care about the details of Raman scattering; or else they would have divulged it in the passage, no?
What they want you to recognize is that in the way they have presented it, Raman scattering is simply a model for an inelastic collision, where A is moving (the photon) and B is initially at rest (the material the photon is being shot into).

Thus, we should just use the equation K2/K1 = mA/mA+mB.

With all that said -- the question is rather ambiguous if you do have significant prior knowledge of Raman scattering and I wouldn't expect to see a question with answer choices that can be so readily confounded by outside knowledge on the MCAT itself.
However; as a rule of thumb, for things that aren't mentioned on the MCAT full content list I do believe it better to go only on what information is given in the passage rather than drawing from previous knowledge. This is stated explicitly: not to use outside knowledge on any obscure topics that you have that may come up in verbal reasoning, in the MCAT full content PDF, however I believe it does in general apply to the rest of the exam as well.

 

[MyNameIsRobertPaulson]

You're definitely correct in stating that Raman scattering can be either Stokes or Anti-Stokes, and thus the photon can either be a lower or higher energy than oron the MCAT itself.

However; as a rule of thumb, for things that aren't mentioned on the MCAT full content list I do believe it better to go only on what information is given in the passage rather than drawing from previous knowledge. This is stated explicitly: not to use outside knowledge on any obscure topics that you have that may come up in verbal reasoning, in the MCAT full content PDF, however I believe it does in general apply to the rest of the exam as well.

I would probably not agree with this. I have answered plenty of Qs using outside knowledge in my science practice so far, even on AAMC questions. I think a good rule of thumb would be to not pick any answer that contradicts known science, but when choosing between 2 answers, pick the one with more direct support from the science passage if you can?

I do agree that this kind of ambiguity would be unlikely to make it into an actual AAMC Q, otherwise we could be arguing for more points!