Results of our PDR modeling for a high density clump in the Orion Bar (n_H = 4 × 10⁶ cm⁻³ and G₀ = 1.17 × 10⁴). In all panels, the abscissa gives visual extinction. Top panel: dependence of the electron abundance (black solid line/ left ordinate), gas temperature (red solid line/ right ordinate), and dust temperature (red line, green dash-dot/ right ordinate). Middle panel: fractional abundances of ionized and neutral carbon and CO as red, black, and blue lines, respectively. Bottom panel: fractional abundances of C₂H, C₂ H⁺, c-C₃ H₂, and c-C₃H as ionized and neutral carbon and CO as blue, black, green, and red lines, respectively.