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As we all know $\ce{H2O}$ is bent ($C_\mathrm{2v}$) in its ground state equilibrium structure, rather than linear ($D_\mathrm{\infty h}$), which can be readily understood e.g. from the MO diagram of bent versus linear case:

H2O at linear geometry

H2O at bent geometry

The question, that puzzles me here, is if that apparent case of "symmetry breaking" can be described by a Jahn-Teller or Renner-Teller effect? Jahn-Teller seemingly is ruled out since the "high symmetric" from is linear, which is excluded from the Jahn-Teller theorem while the Renner-Teller effect is apparently a subtle ro-vibronic effect.

Since the water ground state is a closed shell singlet (even in the linear case), my take on it would be, that it must be a second-order JT-effect of coupling between ground and excited states by virtue of the bending distortion. But I am not sure since I never heard or read about water as a second-order JT-example.

Can anyone comment on that?

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    $\begingroup$ Check out Albright et al. Orbital Interactions in Chemistry 2ed pp 131-9 $\endgroup$ – orthocresol Jan 23 at 12:43
  • $\begingroup$ @orthocresol: So it means: Perfectly normal second order JT, if I understand correctly? $\endgroup$ – Rudi_Birnbaum Jan 23 at 13:40
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    $\begingroup$ I think so, but will refrain from giving a more certain answer, I only briefly flicked through. $\endgroup$ – orthocresol Jan 23 at 14:03

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