Evolutions of CH3CN abundance in molecular clumps

To investigate the effects of massive star evolution on surrounding molecules, we select 9 clumps previously observed with Atacama Pathfinder Experiment (APEX) telescope and Submillimeter Array (SMA) telescope. Based observations APEX, obtain luminosity to mass ratio L$_{\rm clump}$/M$_{\rm clump}$ that range from 10 154 L$_{\sun}$/M$_{\sun}$, where some them embedded Ultra Compact (UC) H\,{\footnotesize II} region. Using SMA, CH$_3$CN (12$_{\rm K}$--11$_{\rm K}$) transitions were toward star-forming regions. We derive rotational temperature column density using XCLASS program, calculate its fractional abundance. find seems increase when is between 40 then decrease $\ge$ L$_{\sun}$/M$_{\sun}$. Assuming gas heated by radiation central star, effective distance relative estimated. The $\sim$ 0.003 0.083 pc, which accounts for 1/100 1/1000 clump size. increases slightly as (R$_{\rm eff}$ (L$_{\rm clump}$)$^{0.5\pm0.2}$). Overall, abundance found evolve, e.g., X$_{\rm CH_3CN}$ clump}$)$^{-1.0\pm0.7}$. steady decline can be interpreted a result photodissociation.