We present a synchrotron-x-ray study of the smectic-C (${\mathrm{S}}_{\mathrm{C}}$) and smectic-I (${\mathrm{S}}_{\mathrm{I}}$) phase in a single-domain freely suspended film. Weak bond-orientational order in the ${\mathrm{S}}_{\mathrm{C}}$ phase evolves continuously into the ${\mathrm{S}}_{\mathrm{I}}$ phase so that the two phases are not thermodynamically distinct. From a Fourier analysis we obtain the hexatic order parameter ${\mathrm{C}}_6$, the coefficient of cos6χ. The higher &, with ${\mathrm{\sigma }}_{\mathrm{n}}$≃n+0.3n(n-1), in agreement with a scaling theory.

• Received 17 April 1986

DOI:https://doi.org/10.1103/PhysRevLett.57.98