The atomic structure of the {beta}-SiC(100)-{ital c}(2{times}2) surface was analyzed using dynamical calculations of low-energy electron-diffraction intensities. The {ital c}(2{times}2) surface was prepared in ultrahigh vacuum by two different methods. The first utilized the removal of surface silicon by high-temperature annealing in ultrahigh vacuum. The second route utilized the deposition of surface carbon by exposing the stoichiometric (2{times}1) surface at 1125 K to C{sub 2}H{sub 4}. Our results showed that both methods produced a surface terminated with C{sub 2} groups in staggered silicon bridge sites. Weak silicon dimer bonds were found in the second atomic layer of the {ital c}(2{times}2) surface produced by silicon sublimation, but not for the {ital c}(2{times}2) surface produced by C{sub 2}H{sub 4} exposure. We postulate that hydrogen, released by the thermal decomposition of C{sub 2}H{sub 4}, saturated silicon dangling bonds in the second atomic layer, suppressing dimer formation.