How do rotational and vibrational energies in molecules depend on masses?

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Discussion Overview

The discussion revolves around the effects of variable masses of elementary particles on the rotational and vibrational energy transitions in molecules. Participants explore theoretical implications and practical considerations related to mass variations in the context of molecular energy states.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant questions how changes in the mass of elementary particles would affect rotational and vibrational energy transitions, seeking clarity on whether these energies would increase, decrease, or remain unchanged.
  • Another participant notes the ambiguity surrounding the treatment of electron masses in vibrational spectra, mentioning that while they should theoretically be handled by the Born-Oppenheimer (BO) expansion, practical approximations often include them due to better empirical results.
  • A further contribution highlights the complexity of the exact formulation of the BO perturbation expansion, referencing a summer school where this topic was discussed and suggesting that it is a non-trivial issue.

Areas of Agreement / Disagreement

Participants express uncertainty regarding the treatment of masses in molecular energy calculations, indicating that multiple competing views remain on how to approach the problem.

Contextual Notes

There are limitations in the discussion regarding the assumptions made about mass variations and their effects, as well as the dependence on specific definitions and approximations in the BO expansion.

meteor84
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Hi!

I'm wondering what the effects of a variable mass of elementary particles on the rotational and vibrational energy-transitions would be like? Would they increase, decrease or stay the same?

Thank you for your help!

Regards
 
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See:

http://www.ulb.ac.be/cpm/people/scientists/bsutclif/bornop.pdf
 
Last edited by a moderator:
On a related note: What to do with the electron masses is not actually so clear. In principle they should be handled by the BO expansion and vibrational spectra should be calculated using bare masses. But in approximate treatments they are often included, because this seems to work better (note: this has an effect of <2 cm^{-1} in most cases).

See http://dx.doi.org/10.1080/00268970701604671 for a deeper discussion of this topic.
 

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