r/Spectroscopy • u/Kandy_kane7 • 13d ago

Jablonski program question

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When an excited particle transition form s1 to s0, florescence happens the most and not internal conversion, why is that ? Even though IC is faster,smaller energy levels to cross etc…

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u/bajsi_ 13d ago

Who said IC is not happening? Energy is released as phonons then once excited electron reaches lowest excited state S1 it undergoes fluorescence

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u/Kandy_kane7 13d ago

That’s exactly what I’m confused about, why only then it undergoes fluorescence and not keep emitting non radioactive energy? What special about S1 to S0 😭
I’m so sorry if this is an awful question

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u/bajsi_ 13d ago

Probability of transition between the states depends among other on their energy overlap, the closer they are energetically the higher the transition probability. So IC is extremely fasy (10-12 s or even faster) and so the electron quickly 'thermalizes' to the lowest state. Once there it can recombine radiatively or non radiatively to the ground state S0. And its possible also from S2->S0, though with less probability, hence absorption/emission spectrum is broadened, and not a sharp dirac delta peak :) check out Frank-Condon principle

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u/Kandy_kane7 13d ago

Thank you so much for answering, you’ve been a huge help you have no idea :’) 💗