Adsorption of fluoroform CHF3 on ice Ih(0001): Structure and vibrations

The adsorption of fluoroform CHF3 on an ice Ih(0001) surface grown on Pt(11 1) under UHV conditions was studied using high resolution elastic and inela stic helium atom scattering. The results indicate that the CHF3 molecules a re aligned with their H-atoms pointing downwards and form an ordered p(1x1) overlayer at temperatures less than T-s=75 K. The Debye temperature decrea ses from Theta(ice)(D)=132 K for the clean ice surface to Theta(CHF3)(D)=53 K on adsorption of one monolayer. From time-of-flight measurements the red uction in Theta(D) appears to be due to a substantial increase in multiphon on processes and the creation of a new, broad, dispersionless, low frequenc y vibrational mode at (h) over bar omega=2.1 meV. (C) 1999 American Institu te of Physics. [S0021-9606(99)71127-X].