The aim is to establish the nature of the surface layer of 8CB at the nematic-air interface by measuring neutron reflection from three differently deuterated versions of 8CB. Nematic-air is the simplest possible homeotropic nematic surface and so represents the baseline for future studies of homeotropic alignment agents for devices. Comparison between the 3 isotopomers will establish the validity of deductions in terms of molecular ordering. There are 3 known possibilities for the smectic like layers characterized by different relationships between wave period, d, and the molecular length, l: (i) partial bilayer as found in the bulk smectic phase of the material (d=1.4l), (ii) monolayer (d=l) and (iii) full bilayer (d=2l). The data will be modeled to determine whether the first surface layer correspond to one of these or a new arrangement.