Rotational and vibrational spectroscopy

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    Rotational Spectroscopy
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SUMMARY

This discussion focuses on the principles of rotational and vibrational spectroscopy, specifically addressing the increase in spacing between rotational energy levels as the rotational quantum number J increases. The participant also clarifies the selection rule for infrared (IR) spectroscopy, stating that Δv=±1 applies primarily to IR light, while electronic transitions using ultraviolet (UV) light can allow for Δv=±0,1. The concept of Franck-Condon progression is introduced, highlighting the series of transitions observed due to differing equilibrium positions of electronic states.

PREREQUISITES
  • Understanding of microwave spectroscopy principles
  • Familiarity with rotational and vibrational energy levels
  • Knowledge of selection rules in spectroscopy
  • Basic concepts of electronic transitions and Franck-Condon factors
NEXT STEPS
  • Study the mathematical derivation of rotational energy levels in microwave spectroscopy
  • Research the implications of selection rules in IR and UV spectroscopy
  • Explore the Franck-Condon principle and its applications in spectroscopy
  • Learn about the differences between IR and UV spectroscopy techniques
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Students and researchers in physical chemistry, particularly those focusing on spectroscopy, molecular physics, and quantum mechanics.

Chemist20
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Hello there!

Im studying microwave spectroscopy, and I'm stuck because I don't see why the spacing between rotational energy levels increases as J does. Can anyone explain please?

Also, about IR, I see everywhere that the selction rule is Δv=±1. Correct me if I'm wrong but I'm guessing that's only when you use IR light. If you where to use UV, where an electronic transition can take place, we could also go from l=1 v=0 to l=2 v=0 and hence Δv=±0,1. (excluding overtones of this) . Is this correct?

Thanks!
 
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In electronic transitions you usually observe a whole series of transitions of possible v values (so called Franck Condon progression) as the equilibrium positions of the electronic ground and excited state do not coincide.
 

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