Lysergic acid diethylamide. Photoelectron ionization potentials as indices of behavioral activity.

The photoelectron spectrum of lysergic acid diethylamide (LSD) reveals five ionization potentials (IP's) between 7.25 and 9.75 eV arising from the aromatic (pi) portion of the molecule and IP's of 8.4 eV arising from the tertiary amine and 8.5-9.0 and 9.1 eV arising from the amide group. Comparisons of the IP's of LSD, and of phenethylamines and tryptamines reported by us elsewhere, with activities of these compounds in rat and human behavioral tests show that increasing activity is paralleled by decreasing IP.