在Sgr B2周围的扩展区域中观察到七个COM的化学分化：CH $_2$ OCHO，CH $_3$ OCHO，t-HCOOH，C $_2$ H $_5$ OH，在扩展区和热核Sgr B2（N）和Sgr B3（N）附近都检测到CH $_3$ NH $_2$ 2（M），而CH $_3$ OCH $_3$和C $_2$ H $_5$ CN仅在热核附近检测到。延伸区的密度和温度相对较低。人们提出了不同的解吸机制来解释寒冷地区观测到的COMs，但未能解释CH $_3$ OCH $_3$和C $_2$ H $_5$ CN的缺乏。我们探索了在什么样的物理条件下，化学模拟可以拟合的观测和解释这些物种的不同空间分布。我们使用蒙特卡罗方法进行详细的参数空间研究。我们研究了不同的机制如何影响结果。所有基于静态物理的气体-颗粒化学模型都不能拟合观测结果。在$T\sim30-60$ K时，基于演化物理条件的计算结果可以拟合6个COMs，但最佳拟合温度仍高于观测到的尘埃温度20 K。当温度为20 K时，考虑短持续时间的$\sim 10^2$ yr X射线爆发与$ζ_{\mathrm{CR}}=1.3\times10^{-13}$ s $^{-1}$，在$T\sim27$ K处达到最好的一致。反应解吸是产生这些COMs并导致CH $_3$ OCH $_3$和C $_2$ H $_5$ CN低丰度的关键机制。Sgr~B2周围扩展区域的演化可能始于冷的$T\le10$ K阶段，随后是升温阶段。当它的温度达到$T\sim20$ K时，获得了来自Sgr A* 的X射线耀斑，其持续时间不超过100年，强烈影响了Sgr B2的化学。观测到的COMs在这样的耀斑发生后仅几百年才保持其观测到的丰度，这可能意味着这种短期X射线耀斑相对频繁地发生。
英文摘要：
The chemical differentiation of seven COMs in the extended region around Sgr B2 has been observed: CH$_2$OHCHO, CH$_3$OCHO, t-HCOOH, C$_2$H$_5$OH, and CH$_3$NH$_2$ were detected both in the extended region and near the hot cores Sgr B2(N) and Sgr B2(M), while CH$_3$OCH$_3$ and C$_2$H$_5$CN were only detected near the hot cores. The density and temperature in the extended region are relatively low. Different desorption mechanisms have been proposed to explain the observed COMs in cold regions but fail to explain the deficiency of CH$_3$OCH$_3$ and C$_2$H$_5$CN. We explored under what physical conditions the chemical simulations can fit the observations and explain the different spatial distribution of these species. We used the Monte Carlo method to perform a detailed parameter space study. We investigated how different mechanisms affect the results. All gas-grain chemical models based on static physics cannot fit the observations. The results based on evolving physical conditions can fit six COMs when $T\sim30-60$ K, but the best-fit temperature is still higher than the observed dust temperature of 20 K. The best agreement at $T\sim27$ K is achieved by considering a short-duration $\sim 10^2$ yr X-ray burst with $ζ_{\mathrm{CR}}=1.3\times10^{-13}$ s$^{-1}$ when the temperature is 20 K. The reactive desorption is the key mechanism for producing these COMs and inducing the low abundances of CH$_3$OCH$_3$ and C$_2$H$_5$CN. The evolution of the extended region around Sgr~B2 may have begun with a cold, $T\le10$ K phase followed by a warm-up phase. When its temperature reached $T\sim20$ K, an X-ray flare from Sgr A* with a short duration of no more than 100 years was acquired, affecting strongly the Sgr B2 chemistry. The observed COMs retain their observed abundances only several hundred years after such a flare, which could imply that such short-term X-ray flares occur relatively often.
The quest for complex molecules in space: Laboratory spectroscopy of n-butyl cyanide, n-C4H9CN, in the millimeter wave region and its astronomical search in Sagittarius B2(N)
