The orbital angular momentum of photons in paraxial beams offers the possibility of arbitrary base-N digits for freespace laser communications. Atmospheric turbulence can cause the orbital angular momentum of photons in a propagating beam to scatter from its original azimuthal mode. The probability of obtaining correct or incorrect measurement of the transmitted orbital angular momentum state after propagation through atmospheric turbulence is calculated from the rotational field correlation (second order field moment). A previously published model of the rotational field correlation for Laguerre-Gaussian beams is limited to the weak turbulence regime and assumes that the turbulence effects can be considered a pure phase perturbation. This model is validated by calculating the same quantity with the extended Huygens-Fresnel integral, valid in all regimes of turbulence. To obtain closed form expressions, a quadratic structure function approximation was applied. The probability of receiving the transmitted orbital angular momentum state was calculated and compared to the existing model. The results indicate that the quadratic structure function approximation leads to a slight overprediction of the probability in the weak turbulence regime. For finite transmitter apertures, the previously published model, with a spherical wave structure function, rather than the plane wave structure function used in the original work, is believed to be the most accurate model in the weak turbulence regime.© (2010) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.