LN Domelsmith investigated the ionization potential energies of LSD and harmala alkaloids. Table II summarizes the first four pi ionization potential energies, ranging from 7.38-10.5 electron volts (eV), for norharmane, harmane, harmol, harmine, and harmaline. Harmaline was the best electron donor in this series, with a first ionization potential energy of 7.38 eV.
Dihydro-harmine (harmaline) and harmine differ by 2 electrons, the saturation of one bond, which in this case changed the energy of the ionization potential by 0.5 eV, a very large quantity.
The trend continues that harmine and harmaline are the most psychoactive in this series of harmala alkaloids, and have the lowest energy ionization potential.
Domelsmith L. N. and K. N. Houk (1978). Photoelectron spectroscopic studies of hallucinogens: the use of ionization potentials in QSAR. NIDA Research Monograph 22, 423-440.