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Ammonia in positively charged pre-nucleation clusters: a quantum-chemical study and atmospheric implications

机译:带正电的预成核簇中的氨:量子化学研究及其对大气的影响

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The quantum-chemical treatment of pre-nucleation clusters consisting ofatmospheric nucleation precursors is critically important for theunderstanding of the molecular nature of atmospheric nucleation. In thepresent study, the influence of ammonia on the thermochemical stability ofpositively charged pre-nucleation clusters has been studied using theDensity Functional Theory (DFT). The formation of binary(NH4+)(H2O)n and ternary(NH4+)(H2SO4)(H2O)n ionic clusters and theconversion of (H3O+)(H2O)n−1 into (NH4+)(H2O)nand (H3O+) (H2SO4)(H2O)n−1 into(NH4+)(H2SO4)(H2O)n have been investigated.The thermochemical analysis carried out in the present study shows both(H3O+)(H2O)n−1→(NH4+) (H2O)n and(H2SO4)(H3O+)(H2O)n−1→(NH4+)(H2SO4) (H2O)ntransformations to befavorable thermodynamically and gives us a clear indication of the importantrole of ammonia in the conversion of positively charged clusters containinghydronium (H3O+) into those containing protonated ammonia. Undertypical continental boundary layer condition, a large fraction of smallpositive ions may contain ammonia, but most of neutral and negative hydratedsulfuric acid monomers do not contain ammonia. In term of absoluteconcentrations, around 1000 cm−3 out of 107 cm−3 of sulfuricacid momoners contain ammonia. (NH4)+(H2O)n clustersappear to dominate the concentrations of small positive ions. Because of theweak affinity of sulfuric acid molecules to (H3O+)(H2O)nand (NH4+)(H2O)n ions (n≤6), the concentrationsof both ammoniated and un-ammoniated sulfuric acid water proton clusters arequite low. The atmospheric implications of the obtained results arediscussed.
机译:由大气成核前体组成的预成核团簇的量子化学处理对于理解大气成核的分子性质至关重要。在本研究中,使用密度泛函理论(DFT)研究了氨对带正电的预成核簇的热化学稳定性的影响。二元(NH 4 + )(H 2 O) n 的形成和三元(NH 4 + )(H 2 SO 4 )(H 2 O) n 离子簇和(H 3 O + )(H 2 < / sub> O) n -1 转换为(NH 4 + )(H 2 O) n 和(H 3 O + )(H 2 SO 4 )(H 2 O) n -1 变成(NH 4 + )(H 2 SO 4 )(H 2 O) n 进行了研究。本研究进行的热化学分析表明(H 3 O + )(H 2 O) n -1 →(NH 4 + )(H 2 O) n 和(H 2 SO 4 )(H 3 O < sup> + )(H 2 O) n -1 →(NH 4 + )(H 2 SO 4 )(H 2 O) n 有利于转化具有热力学性能,并且清楚地表明了氨在将带氢的正电荷簇(H 3 O + )转化为含质子化氨的簇中的重要作用。在典型的大陆边界层条件下,大部分小的正离子可能包含氨,但是大多数中性和负性水合硫酸单体都不含氨。就绝对浓度而言,硫酸类单体中的10 7 cm -3 中大约有1000 cm −3 含有氨。 (NH 4 ) + (H 2 O) n 簇似乎主导了小阳离子的浓度。由于硫酸分子对(H 3 O + )(H 2 O) n 的亲和力弱i> 和(NH 4 + )(H 2 O) n < / sub>离子( n ≤6)时,氨化和未氨化的硫酸水质子簇的浓度都非常低。讨论了所得结果对大气的影响。

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