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I have been studying an emission mechanism that exploits the ionization, disassociation and subsequent fluorescent recombination of nitrogen molecule by a femtosecond laser for velocimetry.

The literature suggests that the femtosecond laser promotes the ‘tunnel ionization’ of the nitrogen molecule rather than the disassociation of the molecule despite the higher ionization energy (15.6 eV) compared to the disassociation energy (9.8 eV).

Since both ionization and disassociation require that the electron absorbs photons that should match the energy requirement, I was just hoping to understand the physics behind the ionization despite the higher energy requirement.

Nikkhil Chander
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  • Have you seen this question and answer ? https://physics.stackexchange.com/questions/491588/what-is-the-real-difference-between-tunneling-ionization-and-multiphoton-ionizat – anna v Feb 24 '24 at 05:39
  • search "physics" here with ionization, with a z . there are a number of questions some of them with answers. – anna v Feb 24 '24 at 05:48
  • Thank you for the reply, Anna. I did look over the article which explains the Keldysh parameter and the different regimes of ionization. My question is why ionization is preferred over disassociation despite the higher energy required for the latter. Also. is it right to infer that during the tunneling process, the election does not absorb any energy to become 'free'. – Nikkhil Chander Feb 24 '24 at 21:53
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    It is a matter of quantum mechanical probabilities. It is not the electron that absorbs energy but the whole atomic structure to which the electron is quantum mechanically bound. – anna v Feb 25 '24 at 05:47
  • Sincerely I think its just about what you are looking at: if you look at electron velocity, then you know that you have to have created ions and ionized the molecule: just dissociation might generate 2 neutral . Also, during the femtosecond irradiation, the nitrogen atoms are practically fixed in space, hence they are still a molecule that you just stripped an electron out of. Later, as the excitation dynamics evolve, the molecule might go through a dissociation path and you might create either $N_2^+$ or $N+N^+$. Its just that femtosecond irradiation is too fast. – José Andrade Feb 25 '24 at 16:04

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