2ND-HARMONIC GENERATION MEASUREMENTS OF MOLECULAR-ORIENTATION AND COADSORPTION AT THE INTERFACE BETWEEN 2 IMMISCIBLE ELECTROLYTE-SOLUTIONS

Resonant optical second harmonic generation (SHG) is obtained from mon olayers of 4-n-octyloxybenzoic acid (OBA) and n-octyl-4-hydroxybenzoat e (OHB) adsorbed at the water/1,2-dichloroethane interface. The polari zation dependence of the SHG from pure monolayers of OBA and OHB indic ates that the molecular axis of the OBA molecules is tilted 6-degrees closer to the surface normal than that of the OHB molecules. The SHG f rom a series of mixed monolayers of OBA and OHB exhibits interference effects that demonstrate that the dipole moments of the coadsorbed mol ecules are oriented in opposite directions at the interface.