Is there sth like rydberg formula for Molecular ionization?
No, it gets more and more complicated. Rydberg formula works only for hydrogen-like atoms (nucleus and one electron).
I guess for some very specific cases similar formulas could be found, but that would be numerology - while one can find some formula for every sequence, it doesn't meant the formula touches on some deeper phenomena as it is in the case of Rydberg's equation.
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