Department of Physics, University of Helsinki , P.O. Box 64, FI-00014, Finland.
J Phys Chem A. 2013 Dec 27;117(51):14109-19. doi: 10.1021/jp4049764. Epub 2013 Dec 13.
Quantum chemical calculations have been performed on negatively charged nitric acid-sulfuric acid-dimethylamine clusters. The cluster energies were combined with a kinetic model to study the chemical ionization of sulfuric acid molecules and sulfuric acid-dimethylamine clusters with nitrate ions. Both the sulfuric acid monomer and the H2SO4·(CH3)2NH cluster get ionized, but the cluster has a much higher dipole moment, and thus a higher collision rate with charger ions. Clustering of sulfuric acid with bases will therefore increase its detection probability in the CIMS, instead of decreasing it as has been suggested previously. However, our comparison of different quantum chemical methods shows some uncertainty on the extent of sulfuric acid-dimethylamine cluster formation in typical ambient conditions, and no experimental data is available for comparison. Apart from affecting CIMS measurements, the degree of clustering is directly linked to the formation rate of larger clusters, and needs to be quantified in order to understand atmospheric new-particle formation. On the basis of the different charging efficiencies of the monomer and the cluster, a method is proposed for determining experimentally the binding energies of H2SO4·base clusters by measuring the extent of cluster formation as a function of base concentration.
已对带负电荷的硝酸-硫酸-二甲胺分子簇进行了量子化学计算。将簇能量与动力学模型相结合，研究了硫酸分子和硫酸-二甲胺与硝酸盐离子的化学电离。硫酸单体和 H2SO4·（CH3）2NH 簇都发生了电离，但簇具有更高的偶极矩，因此与电荷离子的碰撞率更高。因此，与碱基的硫酸簇化将增加其在 CIMS 中的检测概率，而不是像以前所建议的那样降低其检测概率。然而，我们对不同量子化学方法的比较表明，在典型的环境条件下，硫酸-二甲胺簇形成的程度存在一些不确定性，并且没有可用的实验数据进行比较。除了影响 CIMS 测量外，簇化程度还直接与更大簇的形成速率相关，需要对其进行量化，以便了解大气中新粒子的形成。基于单体和簇的不同充电效率，提出了一种通过测量基浓度对簇形成程度的影响来实验确定 H2SO4·碱基簇结合能的方法。
