Verdes Marian, Paniagua M
Departamento de Química Física Aplicada, Facultad de Ciencias, C-14, Universidad Autónoma de Madrid, Cantoblanco, 28049, Madrid, Spain,
J Mol Model. 2015 Apr;21(4):78. doi: 10.1007/s00894-015-2611-7. Epub 2015 Mar 11.
Strong acids such as HCl (C), HNO3 (N) and H2SO4 (S) acquire relevance in Polar Stratospheric Clouds (PSCs) and aerosols in which nucleation processes occur. Ab initio quantum chemical studies of aggregates were performed for these strong acids. Structures were calculated using DFT methods with the B3LYP hybrid functional and aug-cc-pVTZ basis set. As an initial constraint, an H2SO4 moiety was placed in all candidate structures. A total of 11 optimized structures was found: a global minimum (CSN-a) plus ten local minima on the Potential Energy Surface (PES). The global minimum aggregate gave four hydrogen bonds, yielding a hexagonal ring in its structure. HNO3 acts as proton donor in all clusters; nevertheless, using trans-H2SO4 as the proton donor yielded the most stable structures, whereas HCl acts mainly as a proton donor/acceptor. Real harmonic frequencies, IR spectra, and inter-monomeric parameters were obtained. CSN-a symmetric stretching modes were shifted to 2805.56 cm(-1) and 3520.00 cm(-1) for H-Cl modes, while O-H modes shifted to 3256.87 cm(-1) and 3362.47 cm(-1). On the other hand, relative stabilities improved for 5 of the 11 aggregates when the temperature decreased from 298 K to 210 K, 195 K and 188 K. The aggregate CSN-f remained unstable only at 210 K. Moreover, the relative Gibbs free energy, ΔG(0-298K) was -9.26 kcalmol(-1) with respect to CSN-a; relative reaction Gibbs free energy [Δ(ΔG)] values ranged from 0.0 at 298 K, to -6.9 kcalmol(-1) at 188 K. It seems that CSN aggregates remain slightly more stable than CNS aggregates with a HNO3 moiety when the temperature decreases from 298 to 188 K. Five structures remained relatively stable under both study conditions.
诸如HCl（C）、HNO₃（N）和H₂SO₄（S）等强酸在极地平流层云（PSC）和气溶胶中具有重要意义，在这些环境中会发生成核过程。对这些强酸进行了团簇的从头算量子化学研究。使用具有B3LYP混合泛函和aug-cc-pVTZ基组的密度泛函理论（DFT）方法计算结构。作为初始约束，在所有候选结构中都放置了一个H₂SO₄部分。总共发现了11个优化结构：一个全局最小值（CSN-a）加上势能面（PES）上的十个局部最小值。全局最小团簇形成了四个氢键，其结构中形成了一个六边形环。在所有团簇中HNO₃都作为质子供体；然而，使用反式H₂SO₄作为质子供体产生了最稳定的结构，而HCl主要作为质子供体/受体。获得了真实的谐振频率、红外光谱和单体间参数。CSN-a的对称伸缩模式对于H-Cl模式移至2805.56 cm⁻¹和3520.00 cm⁻¹，而O-H模式移至3256.87 cm⁻¹和3362.47 cm⁻¹。另一方面，当温度从298 K降至210 K、195 K和188 K时，11个团簇中有5个的相对稳定性提高。团簇CSN-f仅在210 K时不稳定。此外，相对于CSN-a，相对吉布斯自由能ΔG(0 - 298K)为 -9.26 kcal/mol；相对反应吉布斯自由能[Δ(ΔG)]值范围从298 K时的0.0到188 K时的 -6.9 kcal/mol。当温度从298 K降至188 K时，CSN团簇似乎比带有HNO₃部分的CNS团簇略微更稳定。在两种研究条件下，有五个结构保持相对稳定。
