Determine energy state difference using absorption-emission spectra

AI Thread Summary
The discussion revolves around estimating the energy state difference between the vibrational ground state S0,v=0 and the first excited state S0,v=1 using absorption-emission spectra. The provided solution incorrectly identifies transitions at specific wavelengths, leading to confusion about the correct labeling of fluorescence peaks. Participants argue that the solution should express energy differences in units like eV or cm-1, rather than wavelengths, as energy is inversely proportional to wavelength. Clarifications are sought regarding the transitions and the absence of a v=0→0 transition in the spectra. Overall, there is consensus that the initial solution is misleading and requires correction.
JoJoQuinoa
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Hello,

I was wondering if someone could help clarifying this question.

The question asks to estimate the energy state difference between the vibrational ground state of S0,v=0 and the first excited vibrational ground state S0,v=1 of the spectra below.

The given solution: S1,v=1 -> S0,v=1 at \lambda = 400 nm and S1,v=2 -> S0,v=1 at \lambda = 380 nm.

There are two things I'm confused about the solution:
1) From Figure B, I would assume that the first Fluorescence peak at 380 nm in Figure A corresponds to S1,v=0 -> S0,v=1 and the second peak at 400 nm corresponds to S1,v=0 -> S0,v=2. Larger transition results in higher emission energy or smaller wavelength.

2) Why is S0,v=1 being used as the final state for both peaks?
The S1,v=1 -> S0,v=1 would occur as S1,v=1 ->S1,v=0 ->S0,v=1 and
S1,v=2 ->S1,v=0 ->S0,v=1.
Since S1,v=2 or 1 ->S1,v=0 is internal conversion, wouldn't S1,v=0 ->S0,v=1 for the two transitions give off the same energy?

Thanks in advance!
anthraspec.PNG
peakid.PNG
 
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I don't think the solution matches what the question asks for. Could you write the fully replicated question and the solution? Perhaps, a screenshot/photo of the question and solution?

For example, the question asks for the energy state difference, which means that the solution should be in the units of eV or cm-1 (or Hartree). It doesn't make any sense that the solution is in wavelength (nm) because wavelength is inversely proportional to energy and is not linear. Thus, you can't just add/subtract wavelength differences (unless you know what you are doing).

Also,
1) No, the fluorescence peak at 380 is not S1,v=0 → S0,v=1, and the second peak at 400 nm is not S1,v=0 → S0,v=2. What is your reasoning that you are not seeing any v=0→0 transition?
 
Hi Hayao,
Thank you for your response!

The question was: Use the anthracene absorption and emission spectrum in Figure 8.5 (Figure 1 in this post) to construct a combined Jablonski diagram/absorption/emission spectrum sketch. Label all states and calculate transition energies in cm-1.

The solution provided by the Professor and the one I found on Google were similar and as provided in the original post: S1,v=1 -> S0,v=1 at λ = 400 nm and S1,v=2 -> S0,v=1 at λ = 380 nm. I believe both were mislabeled. I found the figure below from ScienceDirect and I think it is correct.

"No, the fluorescence peak at 380 is not S1,v=0 → S0,v=1, and the second peak at 400 nm is not S1,v=0 → S0,v=2. What is your reasoning that you are not seeing any v=0→0 transition?"

Initially, I labeled the first peak as v=0->0 (overlapping peaks in Absorption and Emission spectrum are v=0->0 transition) and second peak to be v=0->1. I got confused by the solution and modified my answer.

anthraspeccorrect.PNG
 
Yes, that figure is correct.
 
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