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(111) under UHV conditions was studied using high resolution elastic and inelastic helium atom scattering. The results indicate that the CHF3 molecules are aligned with their H-atoms pointing downwards and form an ordered p(1×1) overlayer at temperatures less than Ts=75 K. The Debye temperature decreases from ΘiceD=132 K for the clean ice surface to ΘCHF3D=53 K on adsorption of one monolayer. From time-of-flight measurements the reduction in ΘD appears to be due to a substantial increase in multiphonon processes and the creation of a new, broad, dispersionless, low frequency vibrational mode at ℏω=2.1 meV.