[en] We have used the Submillimeter Array to image, at ∼1.″5 resolution, C₂H $N=3\to <!--\; ???\; -->2$ emission from the circumstellar disk orbiting the nearby (D = 54 pc), ∼8 Myr-old, ∼0.8 $M_{\odot <!--\; ???\; -->}$ classical T Tauri star TW Hya. The SMA imaging reveals that the C₂H emission exhibits a ring-like morphology. Based on a model in which the C₂H column density follows a truncated radial power-law distribution, we find that the inner edge of the ring lies at ∼45 AU, and that the ring extends to at least ∼120 AU. Comparison with previous (single-dish) observations of C₂H $N=4\to <!--\; ???\; -->3$ emission indicates that the C₂H molecules are subthermally excited and, hence, that the emission arises from the relatively warm ($T\gtrsim <!--\; ???\; -->40$ K), tenuous ($n\ll <!--\; ???\; -->{10}^7$ cm⁻³) upper atmosphere of the disk. Based on these results and comparisons of the SMA C₂H map with previous submillimeter and scattered-light imaging, we propose that the C₂H emission most likely traces particularly efficient photo-destruction of small grains and/or photodesorption and photodissociation of hydrocarbons derived from grain ice mantles in the surface layers of the outer disk. The presence of a C₂H ring in the TW Hya disk hence likely serves as a marker of dust grain processing and radial and vertical grain size segregation within the disk.