We present observations of CH _ { 3 } CN ( 12 - 11 ) emission at a resolution of \sim 2″ toward the shell-like ultracompact H II region G5.89 - 0.39 with the Submillimeter Array . The integrated CH _ { 3 } CN emission reveals dense and hot molecular cocoon in the periphery of the H II region G5.89 - 0.39 , with a CH _ { 3 } CN deficient region roughly centered at G5.89 - 0.39 . By analyzing the CH _ { 3 } CN emission using population diagram analysis , we find , for the first time , a decreasing temperature structure from 150 to 40 K with the projected distance from Feldt ’ s star , which is thought to be responsible for powering the H II region . Our results further indicate that the majority of the heating energy in the observed dense gas is supplied by the Feldt ’ s star . From the derived CH _ { 3 } CN column density profile , we conclude that the dense gas is not uniformly-distributed but centrally-concentrated , with a power-law exponent of 5.5 for r \lesssim 8000 AU , and 2.0 for 8000 AU \lesssim r \lesssim 20000 AU , where r is the distance to Feldt ’ s star . The estimated large power index of 5.5 can be attributed to an enhancement of CH _ { 3 } CN abundance in the close vicinity of Feldt ’ s star .