Why is ionization energy measured in gaseous phase?

When I looked up the definition of ionization energy, it says:-



> 
> it is the energy required to remove one electron from the shell to
>  infinity in an atom in gaseous state.
> 
> 
> 


Why is it measured in gaseous phase and not in any other phase?




You want to determine the energy for a **single molecule** and avoid stabilization effects through intermolecular interactions.


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