Surface crystallization of liquid n-alkanes and alcohol monolayers studied by surface vibrational spectroscopy

Infrared-visible sum-frequency generation (SFG) has been used to obtain the surface vibrational spectra of CH stretches for liquid n-eicosane and a monolayer film of 1-dodecanol in equilibrium with an excess drop on water. The SFG data for surface freezing of eicosane represent a unique study of ordering among nonpolar surface molecules and are consistent with the formation of a solid monolayer of nearly vertical, all-trans molecules at the free liquid surface. For the dodecanol film, the result indicates that the alcohol molecules are nearly all-trans and erect both before and after surface crystallization.