Knowledge Bank

Electrons ejected from gaseous molecules by monochromatic radiation $h\nu$, have energies $Ei$, such that $$E_{i}=h\nu-\Delta E_{vib}$$ where $Ii$ is the adiabatic ionization potential of the electron removed, and $\Delta Evib$ represents the changes in the vibrational levels of the molecule being ionized. The apparatus used in determining these energies$\mathrm{<mrow\; data-mjx-texclass="ORD">1</mrow>}$ utilizes a He(I) 584{\AA} (21.22 eV) light source, and a $127\circ$ electrostatic electron velocity analyzer. An energy resolution (half-width at half height) of 0.015 eV for 10 volt electrons is obtainable. Many results obtained have already been $published.2,3$ The spectra of $NH3,SO2$ and $H2S$ all show extensive vibrational fine structure in some or all of the electronic states of the positive ion below 21.22 eV, and ionization potentials accurate to $\pm 0.01$ eV have been measured up to this value. The results are discussed in terms of the electronic structure of the molecules, the bonding characteristics of the various molecular orbitals, and in the light of previously published data concerning the ground and excited ionic states.