For 10 points, name this quantity, the amount of energy required to strip an electron away from a molecule.
For Rydberg states, this quantity over hc is the y-intercept of a plot of wavenumber versus one over n squared. The vertical form of this quantity assumes no change in bond length and is greater than its adiabatic form. This quantity is roughly equal to the negative energy of the highest occupied molecular orbital. Photoelectron spectroscopy measures this quantity for materials. This quantity unexpectedly drops between nitrogen and oxygen due to the stability of half-full subshells. Mulliken averaged this quantity and electron affinity to calculate electronegativity. This quantity is analogous to the wavefunction of a metal, and it usually increases across a row on the Periodic Table. For 10 points, name this quantity, the amount of energy required to strip an electron away from a molecule.
For Rydberg states, this quantity over hc is the y-intercept of a plot of wavenumber versus one over n squared.
ionization energy [or ionization potential]