论文标题
在原恒星信封中碳质晶粒的实验室类似物表面上的氨基甲酸酯的热形成
Thermal formation of ammonium carbamate on the surface of laboratory analogues of carbonaceous grains in protostellar envelopes and planet-forming disks
论文作者
论文摘要
我们组最近证明了灰尘表面在热反应CO2 + 2NH3 $ \ rightarrow $ NH4 + NH2COO中的催化作用。与在KBR上测得的反应速率系数相比，测量纳米尺寸碳和硅酸盐晶粒表面上的反应的速率系数高达三倍。在这项研究中，在50-80 K的延长温度范围内对碳颗粒和KBR进行了反应，并加入了水冰。与KBR上的相应冰层相比，发现晶粒的反应激活能的晶粒低约3倍。因此，尘埃表面在研究反应中的催化作用可能与反应屏障的降低有关。向NH3加入水：谷物上的二氧化碳冰减慢了反应。在H2O：二氧化碳比为5：1时，在实验时间尺度上未检测到反应。该结果提出了质疑氨基甲酸铵在密集的分子云中的热形成，以及具有主导水冰地幔化学的原始环境和原恒星环境的外部区域。但是，它仍然可以发生在晶冰的原始环境和原球环境的内部区域。
The catalytic role of dust grain surfaces in the thermal reaction CO2 + 2NH3 $\rightarrow$ NH4+NH2COO was recently demonstrated by our group. The rate coefficients for the reaction at 80 K on the surface of nanometre-sized carbon and silicate grains were measured to be up to three times higher compared to the reaction rate coefficients measured on KBr. In this study, the reaction was performed on carbon grains and on KBr in the extended temperature range of 50 - 80 K and with the addition of water ice. The reaction activation energy was found to be about 3 times lower on grains compared to the corresponding ice layer on KBr. Thus, the catalytic role of the dust grain surface in the studied reaction can be related to a reduction of the reaction barrier. Addition of water to NH3:CO2 ice on grains slowed the reaction down. At the H2O:CO2 ratio of 5:1, the reaction was not detected on the experimental timescale. This result calls into question the thermal formation of ammonium carbamate in dense molecular clouds and outer regions of protostellar and protoplanetary environments with dominating water ice mantle chemistry. However, it can still happen in inner regions of protostellar and protoplanetary environments in crystalline ices.
