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An intercomparison of different aerosol chemical characterization techniques has been performed as part of a chamber study of biogenic secondary organic aerosol (BSOA) formation and aging at the atmosphere simulation chamber SAPHIR (Simulation of Atmospheric PHotochemistry In a large Reaction chamber). Three different aerosol sampling techniques – the aerosol collection module (ACM), the chemical analysis of aerosol online (CHARON) and the collection thermal-desorption unit (TD) were connected to proton transfer reaction time-of-flight mass spectrometers (PTR-ToF-MSs) to provide chemical characterization of the SOA. The techniques were compared among each other and to results from an aerosol mass spectrometer (AMS) and a scanning mobility particle sizer (SMPS). The experiments investigated SOA formation from the ozonolysis of β-pinene, limonene, a β-pinene–limonene mix and real plant emissions from Pinus sylvestris L. (Scots pine). The SOA was subsequently aged by photo-oxidation, except for limonene SOA, which was aged by NO3 oxidation. Despite significant differences in the aerosol collection and desorption methods of the PTR-based techniques, the determined chemical composition, i.e. the same major contributing signals, was found by all instruments for the different chemical systems studied. These signals could be attributed to known products expected from the oxidation of the examined monoterpenes. The sampling and desorption method of ACM and TD provided additional information on the volatility of individual compounds and showed relatively good agreement. Averaged over all experiments, the total aerosol mass recovery compared to an SMPS varied within 80 ± 10, 51 ± 5 and 27 ± 3 % for CHARON, ACM and TD, respectively. Comparison to the oxygen-to-carbon ratios (O : C) obtained by AMS showed that all PTR-based techniques observed lower O : C ratios, indicating a loss of molecular oxygen either during aerosol sampling or detection. The differences in total mass recovery and O : C between the three instruments resulted predominantly from differences in the field strength (E∕N) in the drift tube reaction ionization chambers of the PTR-ToF-MS instruments and from dissimilarities in the collection/desorption of aerosols. Laboratory case studies showed that PTR-ToF-MS E∕N conditions influenced fragmentation which resulted in water and further neutral fragment losses of the detected molecules. Since ACM and TD were operated in higher E∕N than CHARON, this resulted in higher fragmentation, thus affecting primarily the detected oxygen and carbon content and therefore also the mass recovery. Overall, these techniques have been shown to provide valuable insight on the chemical characteristics of BSOA and can address unknown thermodynamic properties such as partitioning coefficient values and volatility patterns down to a compound-specific level.

Sekundare Organische Aerosole (SOA), welche durch die Oxidation von fluchtigen organischen Verbindungen (VOCs) in der Atmosphare gebildet werden, spielen eine Schlusselrolle bezuglich des Klimawandels und der Luftqualitat. Tausende organische Substanzen sind an der Bildung von SOA beteiligt, weshalb die chemische Charakterisierung von organischen Aerosolen (OA) weiterhin eine grose Herausforderung an die Analytik darstellt. Die Definition der Parameter, die bestimmen wie sich organische Molekule zwischen der Gasphase und der Partikelphase verteilen, ist essentiell, da ihre atmospharischen Lebenszeiten und damit ihr Einfluss stark davon abhangen in welcher Phase sie vorliegen. In dieser Arbeit wurde das sogenannte Aerosol Collection Module (ACM) verbessert, automatisiert und eingesetzt, um eine bessere Charakterisierung von SOA, welches aus Oxidationsprodukten von biogenen Vorlaufersubstanzen gebildete wurde, zu erreichen. Eine Vergleichsstudie des ACM mit anderen Techniken zur chemischen Charakterisierung von SOA wurde durchgefuhrt, bei der der Fokus auf der Bestimmung der Partitionierung biogenen Oxidationsprodukten zwischen der Gasphase und Partikelphase lag. Die eingesetzten Instrumente waren der ACM, die „collection thermal desorption unit“ (TD) und der „chemical analysis of aerosol on-line“ (CHARON), welches verschiedene Aerosolsammler sind, die ein gekoppeltes Proton-Transfer-Reaktion Massenflugzeitspektrometer (PTR-ToF-MS) zur Detektion verwenden. Diese Instrumente wurden an der Atmospharensimulationskammer SAPHIR eingesetzt, um die Bildung und die Alterung von SOA aus verschiedenen Monoterpenen (β-Pinen, Limonen) und realen Pflanzenemissionen (Pinus sylvestris L.) zu untersuchen. Die Charakteristiken der PTR-basierten Instrumente wurden untereinander und mit den Ergebnissen eines Aersolmassenspektrometers und eines SMPS-Spektrometers verglichen. Die Werte der Partitionierung von einzelnen Ionen zwischen der Gas- und Partikelphase, ausgedruckt durch die Massensattigungskonzentration (C*), wurde uber die gleichzeitige Messung der Ionen in der Gas- und Partikelphase bestimmt. Trotz der deutlichen Unterschiede der PTR-basierten Instrumente in den Methoden wie Aerosole gesammelt und desorbiert werden, war die Bestimmung der chemischen Zusammensetzung, d.h. die Ionen die den Hauptanteil zum Signal beigetragen haben, fur die verschiedenen System vergleichbar. Diese Ionen konnten als Hauptoxidationsprodukten von den untersuchten Monoterpenen identifiziert werden. Gemittelt uber alle Experimente war die Wiederfindungsrate der Aerosolmasse verglichen mit dem SMPS-Spektrometer 80 ± 10% fur CHARON, 51 ± 5% fur den ACM und 27 ± 3% fur den TD. Der Vergleich des Sauerstoff zu Kohlenstoff Verhaltnisses (O:C) vom AMS zu den PTR-basierten Instrument zeigte, dass all PTR-basierten Instrument ein niedrigeres Verhaltnis gemessen haben. Das deutet auf einen Verlust von molekularem Sauerstoff hin, der entweder wahrend der Sammlung oder der Desorption verloren geht. Die Unterschiede der Wiederfindungsrate der Aerosolmasse und des O:C Verhaltnisses zwischen den drei PTR-basierten Instrumente konnte hauptsachlich auf Unterschiede in dem Verhaltnis von der elektischen Feldstarke (V cm-1) zu der Dichte des Puffergases (Molekule cm-3) (E/N) in der Laufzeitionisationsrohre des PTR-MS und den Unterschieden in der Sammlung und Desorption der Aerosole zuruckgefuhrt werden. Eine Methode zur Identifizierung von Ionen, die von thermischer Dissoziation wahrend der Desorbtion und der ionischen Dissoziation wahrend der Ionisierung im PTR-MS betroffen waren, wurde entwickelt und getestet. Die Ionen, die nach Anwendung dieser Methode als nicht betroffen identifiziert wurden, wurden auf das zweidimensionale Volatilitatssystem (2D-VBS) abgebildet. Die Ergebnisse zeigen eine Abnahme von C* mit zunehmendem Oxidationsgrad. Fur Substanzen die mit den PTR-basierten Instrumenten gemessen und in fruheren Studien schon identifiziert wurden, wurden weitere Vergleiche mit theoretischen Berechnungen durchgefuhrt. Die theoretischen Berechnungen von C* basieren auf der Molekulstruktur der identifizierten Substanzen und zeigen eine gute Ubereinstimmung mit den experimentell gemessen C* im Bereich von 100 to 102.5. Im Gegensatz dazu liegen im Bereich von C* > 102.5 die theoretischen Berechnung von C* bis zu einem Faktor von 300 uber den gemessen Werten. Diese Unterschiede im Bereich von C* > 102.5 deuten auf (i) mogliche Interferenzen durch thermische und ionische Fragmentierung von Molekulen mit hohen Molekulargewichten hin, welche durch Oligomerization und Akkretion gebildet werden und dann durch Fragmentierung im messbaren m/z-Bereich des PTR-MS gemessen werden sowie (ii) kinetische bedingte Verschiebungen in der Verteilung zwischen Gas- und Partikelphase mit dem Schwerpunkt auf der Kondensation und der irreversiblen Aufnahme von Substanzen in die Partikelphase.

The geometries of gold clusters doped with two phosphorus atoms, Au n P 2 - (n = 1–8), were investigated using density functional theory (DFT) methods. Various two-dimensional (2D) and three-dimensional (3D) structures of the doped clusters were studied. The results indicate that the structures of dual-phosphorus-doped gold clusters exhibit large differences from those of pure gold clusters with small cluster sizes. In our study, as for Au 6 P 2 - , two cis–trans isomers were found. The global minimum of Au 8 P 2 - presents a similar configuration to that of Au 20 - , a pyramid-shaped unit, and the potential novel optical and catalytic properties of this structure warrant further attention. The higher stability of Au n P 2 - clusters relative to Au n + 2 - (n = 1–8) clusters was verified based on various energy parameters, and the results indicate that the phosphorus atom can improve the stabilities of the gold clusters. We then explored the evolutionary path of Au n P 2 - (n = 1–8) clusters. We found that Au n P 2 - clusters exhibit the 2D–3D structural transition at n = 6, which is much clearer and faster than that of pure gold clusters and single-phosphorus-doped clusters. The electronic properties of Au n P 2 - (n = 1–8) were then investigated. The photoelectron spectra provide additional fundamental information on the structures and molecular orbitals shed light on the evolution of Au n P 2 - (n = 1–8). Natural bond orbital (NBO) described the charge distribution in stabilizing structures and revealed the strong relativistic effects of the gold atoms.

Au2P3, the only metastable binary phase of gold phosphide, has been discovered to exhibit remarkable semiconductor properties among metal phosphides. A systematic study on the geometry, the transformation of Au2P3 into different valence states and the different interactions among the atoms of the species is performed by using the density functional theory (DFT) method. The global minimum of Au2P3− is a 3D structure with Cs symmetry. This structure could be distorted from a planar configuration of Au2P3 which decreases the steric effect on it and leads to a new stable configuration. An analogous planar configuration, a local minimum rather than a global minimum, is also found in Au2P3+, due to the electron effect acting on the structure. Natural bond orbital (NBO) analysis reveals the re-distribution progression of the charge within the species. The central located Au atom and another no. 5 positioned P atom play significant roles on the structures. P5, as an electron adjuster, balances the electron distribution at different valence states of the structures. Deformation density analysis supplies information about charge transfer and the bonding type between two adjacent atoms as well. Looking deep into the bonding types, as electron localization function (ELF) suggests, the interaction between two adjacent P atoms (P3 and P4) of Au2P3 belongs to a strong covalent bond. The Au–P interactions among the configurations could be classified as weak classical covalent bonds through the atoms in molecules (AIM) dual parameter analysis. And for the first time, the weak interaction between the two adjacent Au atoms (Au1 and Au2) of the charged states of Au2P3 (Au2P3− and Au2P3+), are verified and different from the neutral Au2P3 through the reduced density gradient (RDG) analysis.

Gold sulfur clusters have received much attention because of the dramatic effect that the gold–sulfide interaction produces in thiol-passivated gold nanoparticles. We present a systematic theoretical study of the electronic properties and geometric structures of AuxS0,±1 (x = 1–10) clusters using the basin-hopping global optimization technique coupled with density functional theory (DFT-BH) methods. Higher-level ab initio calculations are performed to aid in structural assignment. The same species with different electric charges possess different configurations. The 2D-to-3D structural transitions of the global minimum structures of cationic, neutral, and anionic AuxS clusters are found at the sizes of x = 3, 6, and 9, respectively. It is found that the Au5S cluster can be regarded as the building-block unit for the evolution of larger Au–S clusters. The tendency toward planarity of each Au–S cluster species, which is similar to that of bare Au clusters, may be attributed to the strong relativistic effects of Au and the similar electronegativity between Au and S. The trends of the binding energies, electron affinities, and bond parameters with increasing cluster size are studied in detail for each species. The results demonstrate that the binding energies and second-order differences exhibit interesting oscillatory behaviors; it is believed that anionic clusters may be the most suitable for catalysis.

Although ammonium ion-water clusters are abundant in the biosphere, some information regarding these clusters, such as their growth route, the influence of temperature and humidity, and the concentrations of various hydrated clusters, is lacking. In this study, theoretical calculations are performed on ammonium ion-water clusters. These theoretical calculations are focused on determining the following characteristics: (1) the pattern of cluster growth; (2) the percentages of clusters of the same size at different temperatures and humidities; (3) the distributions of different isomers for the same size clusters at different temperatures; (4) the relative strengths of the noncovalent interactions for clusters of different sizes. The results suggest that the dipole moment may be very significant for the ammonium ion-water system, and some new stable isomers were found. The nucleation of ammonium ions and water molecules is favorable at low temperatures; thus, the clusters observed at high altitudes might not be present at low altitudes. High humidity can contribute to the formation of large ammonium ion-water clusters, whereas the formation of small clusters may be favorable under low-humidity conditions. The potential energy surfaces (PES) of these different sized clusters are complicated and differ according to the distribution of isomers at different temperatures. Some similar structures are observed between NH4(+)(H2O)n and M(H2O)n (where M represents an alkali metal ion or water molecule); when n = 8, the clusters begin to form the closed-cage geometry. As the cluster size increases, these interactions become progressively weaker. The successive binding energy at the DF-MP2-F12/VDZ-F12 level is better than that at the PW91PW91/6-311++G(3df, 3pd) level and is consistent with the experimentally determined values.

While atmosphere is known to contain a significant fraction of organic substance and the effect of acetic acid to stabilize hydrated sulfuric acids is found to be close that of ammonia, the details about the hydration of (CH3COOH)(H2SO4)2 are poorly understood, especially for the larger clusters with more water molecules. We have investigated structural characteristics and thermodynamics of the hydrates using density functional theory (DFT) at PW91PW91/6-311++G(3df,3pd) level. The phenomena of the structural evolution may exist during the early stage of the clusters formation, and we tentatively proposed a calculation path for the Gibbs free energies of the clusters formation via the structural evolution. The results in this study supply a picture of the first deprotonation of sulfuric acids for a system consisting of two sulfuric acid molecules, an acetic acid molecule, and up to three waters at 0 and 298.15 K, respectively. We also replace one of the sulfuric acids with a bisulfate anion in (CH3COOH)(H2SO4)2 to explore the difference of acid dissociation between two series of clusters and interaction of performance in clusters growth between ion-mediated nucleation and organics-enhanced nucleation.

We report a joint experimental and theoretical study on the structures of a series of gold clusters doped with a sulfur atom, Au(x)S(-) (x = 2-5). Well-resolved photoelectron spectra are obtained and compared with theoretical results calculated using several density functional methods to elucidate the structures and bonding of Au(x)S(-) (x = 2-5). Au2S(-) is found to have an asymmetric linear global minimum structure with C(∞v) symmetry, while the most stable structure of neutral Au2S is bent with C(2v) symmetry, reminiscent of H2S. Au3S(-) is found to have an asymmetric bent structure with an Au-S-Au-Au connectivity. Two isomers are observed experimentally to co-exist for Au4S(-): a symmetric bent 1D structure (C(2v)) and a 2D planar low-lying isomer (C(s)). The global minimum of Au5S(-) is found to be a highly stable planar triangular structure (C(2v)). Thus, a 1D-to-2D structural transition is observed in the Au(x)S(-) clusters as a function of x at x = 4. Molecular orbital analyses are carried out to obtain insight into the nature of the chemical bonding in the S-doped gold clusters. Strong covalent bonding between S and Au is found to be responsible for the 1D structures of Au(x)S(-) (x = 2-4), whereas delocalized Au-Au interactions favor the 2D planar structure for the larger Au5S(-) cluster.

A theoretical study was performed of the reactions of the stabilized Criegee intermediates (sCIs) of β-pinene with H2O and its dimer. Due to the large size of the biogenic sCIs, the transition states of the hydration reactions were explored with the Monte Carlo Transition State Search Program (MCTSSP), which integrated the Monte Carlo sampling technique with a transition state optimization method. The computations were performed with the M06-2X/6-311+G(2d,p) and B3LYP/6-311+G(2d,p) levels of theory. The relative energies showed that the results of the M06-2X functional are in good agreement with the results of the DF-MP2 and CCSD(T) methods. Both the reactions of the β-pinene-sCI with H2O and the β-pinene-sCI with (H2O)2 were found to be strongly exothermic. Activation barrier calculations indicate that the sink reaction with the water dimer may proceed significantly faster than the reaction with the water monomer despite the low concentration of water dimers in the atmosphere. Therefore, the reaction of sCIs with water vapor that includes large water clusters rather than single water molecules should be studied.

The geometries of phosphorus-doped gold clusters, AunP− (n = 1–8), have been investigated using different density functionals and basis sets. B3LYP and PBE functionals with 4 basis sets (aug-cc-pVDZ, 6-311++G**, CRENBL ECP and LANL2DZ ECP) are chosen for geometry optimisation. Many low-lying structures are obtained for anionic AunP− clusters. For AunP− (n = 1–7) clusters, each level gives the same global minimum structure. It is found that the evolutionary path of phosphorus-doped gold clusters differs from that of pure gold clusters. Phosphorus atoms induce changes in the structure of pure gold clusters in small cluster sizes. Various 2D–3D structures of doped clusters are also investigated. Clusters with an odd number of gold atoms tend to yield planar 2D structures, while those with an even number of gold atoms tend to yield 3D structures.