Is it possible to ionize a molecule?

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Discussion Overview

The discussion centers around the possibility of ionizing a molecule, specifically O2, and the implications of such ionization on its bonding and ionization potential. Participants explore theoretical aspects, calculations related to ionization, and the behavior of ionized molecules.

Discussion Character

  • Exploratory
  • Technical explanation
  • Mathematical reasoning

Main Points Raised

  • One participant questions whether it is necessary to break the O2 bond to create two positively charged oxygen atoms and expresses doubt about the possibility of ionizing O2 while maintaining its bond.
  • Another participant asserts that singly-ionized O2 can still bond, highlighting the role of electron excitation and vibrational energy in the ionization process.
  • A participant raises a question about the calculation of the first ionization energy for O2 compared to O, suggesting that it may not be straightforward and implying the need for a different formula.
  • Another participant agrees that the ionization potential of O2 is likely smaller than that of O, citing the distribution of charge over two atoms as a stabilizing factor and referencing the complexity of calculating ionization potentials using quantum mechanics.

Areas of Agreement / Disagreement

Participants express differing views on the ionization process of O2 and whether it can remain bonded after ionization. There is also a lack of consensus on the calculation of ionization energies, with some suggesting it is more complex for O2 than for O.

Contextual Notes

Participants mention the need for quantum-mechanical descriptions for accurate calculations of ionization potentials and the implications of charge distribution, but do not resolve the specifics of these calculations.

menergyam
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If I have O2, and I want to make it positively charged, don't I have to break the O2 bond and then ionize the two oxygen elements to get two positively charged Oxygen atoms? Is it possible to take away an electron from O2 and still have the O2 be bonded? It is not possible right?
 
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It's possible. Singly-ionized O2 will still bond. Even singly-ionized H2 bonds. It's more a question of whether you excite electrons into the anti-bonding \pi^\star orbital, or transfer a large amount of vibrational energy to the molecule while ionizing it.

That said, O2+ won't stay ionized for very long if it has the chance to grab an electron from some other, less electronegative, atom.
 
Cool. So to calculate the first ionization for O2, would it be the same as the first ionization for O? I really don't think its that simple. There must be a different formula, right?
 
menergyam said:
Cool. So to calculate the first ionization for O2, would it be the same as the first ionization for O? I really don't think its that simple. There must be a different formula, right?

Yes, the IP of O2 should be smaller than for O. This is easily predicted since the molecule has more electrons to counter the charge, and secondly, the charge can be distributed over two atoms instead of one. (And it's a general chemical principle that the more distributed a charge is, the more stable it is, i.o.w. less energy)

Ionization potentials (with the single exception of the hydrogen atom) can't be calculated using any simple formula. You need the quantum-mechanical description of the system. It's roughly equal to the energy of the HOMO (Highest occupied molecular orbital) when calculated using the Hartree-Fock method (Koopmans' theorem), due to some rather nifty error cancellations.
 
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