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As an important contributor to the atmospheric SOA formation, the oxidation of the sesquiterpenes including α-Cedrene are widely considered to play a significant role in atmospheric chemistry, especially for the HOMs formation. Comparable concentrations of the sesquiterpenes (SQTs) detected over the marine boundary layer as those of in terrestrial ecosystems in recent atmospheric campaign, which aroused extensive concern of the SQTs oxidation and its impact on SOA formation in the marine atmosphere. In this work, we comprehensively investigated the oxidation of a representative sesquiterpene (α-Cedrene) initiated by OH, Cl, ClO and BrO radicals and the resulting HOMs formation. For the initial reactions, OH/Cl/ClO/BrO addition reactions are favored over H-atom abstractions by these radicals from the thermodynamic aspect. Seven main first-generation products yielded from the sequential oxidation of the addition adducts by O 2 and NO/HO 2 radical under different atmospheric conditions, such as 2-acetyl-1,1,4-trimethyloctahydropentalene-3a-carbaldehyde. Furthermore, three pathways of the HOMs formation were proposed and compared, (1) autoxidation, (2) multiple H abstractions by OH, Cl, ClO and BrO radicals and the succeeding reactions with HO 2 , and (3) the sequential association reaction of peroxy radicals and OH radical to form ROOOH. For the HOMs formation from the oxidation of α-Cedrene by OH and BrO radicals, the pathway (2) and (3) are thermodynamically feasible under the atmospheric conditions. As most of the H abstractions by Cl and ClO radicals could be difficult to occur, the produced HOMs with more than four or five oxygen atoms could be restricted. To our knowledge, this is the first report for clarifying the oxidation processes of SQTs in the marine atmosphere, which would contribute to the evaluation of the impacts of biogenic volatile organic compounds on the Marine atmosphere. [Display omitted] • The atmospheric oxidation of α-Cedrene by OH, Cl, ClO and BrO radical was clarified. • The first-generation products of α-Cedrene oxidation were elaborated. • The oxidation processes of SQTs initiated by halogen radicals were first studied. • The HOMs formation mechanisms from α-Cedrene oxidation were proposed in marine air. [ABSTRACT FROM AUTHOR]

(E)-β-farnesene is one of the acyclic sesquiterpenes, whose atmospheric oxidation has been determined as a significant contributor to SOA formation due to the formed highly oxidized multifunctional molecules (HOMs). In this work, the atmospheric oxidation of (E)-β-farnesene initiated by OH radical was comprehensively investigated using quantum chemical calculation. For the initial reactions, OH addition reactions are dominant over H atom abstraction reactions because of lower free energy barriers. The first-generation products involving acetone, (E)− 4-methyl-8-methylenedeca-4,9-dienal, 4-methylenehex-5-enal (P3), 6-methylhept-5-en-2-one (P4), formaldehyde, (E)− 7,11-dimethyldodeca-1,6,10-trien-3-one and (E)− 6,10-dimethyl-2-methyleneundeca-5,9-dienal are produced from the subsequent reactions of the OH-(E)-β-farnesene adducts with NO and HO 2. The second-generation products, such as 4-oxopentanal, 4-methylenehex-5-enal, (E)− 4-methyl-8-oxodeca-4,9-dienal, formaldehyde and (E)− 4-methyl-8-methylenenon-4-enedial, are also determined from the successive oxidations of P2 and P3 under high and low NOx conditions. For the formation of HOMs, the H atom shift is the bottleneck for the autooxidation mechanism while our newly proposed mechanism, i.e. the multiple H abstractions by OH radical and reactions with O 2 and HO 2 , is a more thermodynamically favorable formation pathway of the HOMs. Due to the intricate oxidation mechanisms and products, it is difficult to comprise the oxidation mechanisms of sesquiterpenes (including (E)-β-farnesene) in the atmospheric chemical models to thoroughly evaluate their contributions to SOA formation. We expect that this comprehensive oxidation mechanism of (E)-β-farnesene from a theoretical perspective would be conducive to clarifying the atmospheric fate of (E)-β-farnesene and even sesquiterpenes. • The atmospheric oxidation of (E)-β-farnesene by OH radical was comprehensively investigated. • The first- and second-generation oxidation products were clarified. • A new formation mechanism of HOMs from (E)-β-farnesene oxidation was proposed. [ABSTRACT FROM AUTHOR]

The performance of the novel ammonium chemical ionization time of flight mass spectrometer (NH 4 + -CI3–TOF) utilizing NH 4 + adduct ion chemistry to measure first generation oxidized product molecules (OMs) as well as highly oxidized organic molecules (HOMs) was investigated for the first time. The gas-phase ozonolysis of cyclohexene served as a first test system. Experiments have been carried out in the TROPOS free-jet flow system at close to atmospheric conditions. Product ion signals were simultaneously observed by the NH 4 + -CI3-TOF and the acetate chemical ionization atmospheric pressure interface time of flight mass spectrometer (acetate-CI-API-TOF). Both instruments are in remarkable good agreement within a factor of two for HOMs. For OMs not containing an OOH group the acetate technique can considerably underestimate OM concentrations by 2–3 orders of magnitude. First steps of cyclohexene ozonolysis generate ten different main products, detected with the ammonium-CI3-TOF, comprising 93% of observed OMs. The remaining 7% are distributed over several minor products that can be attributed to HOMs, predominately to highly oxidized RO 2 radicals. Summing up, observed ammonium-CI3-TOF products yield 5.6 × 10 9 molecules cm − ³ in excellent agreement with the amount of reacted cyclohexene of 4.5 × 10 9 molecules cm − ³ for reactant concentrations of [O 3 ] = 2.25 × 10 12 molecules cm − ³ and [cyclohexene] = 2.0 × 10 12 molecules cm − ³ and a reaction time of 7.9 s. NH 4 + adduct ion chemistry is a promising CIMS technology for achieving carbon-closure due to the unique opportunity for complete detection of the whole product distribution including also peroxy radicals, and consequently, for a much better understanding of oxidation processes. [ABSTRACT FROM AUTHOR]

Recent ambient atmospheric measurements have observed highly oxygenated organic molecules (HOMs) at a number of sites. Monoterpenes, in particular, are inclined to autoxidize to form HOMs with different oxidants such as OH and O 3. However, little is known about the formation and nucleation of the HOMs in the presence of water (W). In this study, we investigated oxidation mechanism of O 3 addition to limonene in the gas and water phase by theoretical chemistry calculations. Besides, the mechanism of the formation of HOMs from photochemical reactions of limonene and the role of HOMs in new particle formation (NPF) with aerosol nucleation precursors, including sulfuric acid (SA), W and ions were investigated by means of molecular dynamics (MD) simulations and theoretical chemistry calculations. The rate constants of initiation reactions for O 3 addition to limonene are suppressed as the temperature increases. In the process of ion-induced nucleation, HOMs can dominate the initial nucleation steps. The MD results indicated that HOMs can self-aggregate into clusters and W molecules are beneficial to promote the NPF of HOMs. In addition, the nucleation ability of HOMs have significant correlation with the oxygen-to-carbon (O/C) ratio of HOMs. The theoretical results proved the neglected autoxidation pathways including (i) the formation of an endoperoxide moiety in HOMs (ii) a CO2 elimination in presence of an unsaturated peroxy acyl radical. The current study provide valuable insight into NPF mechanism of (HOMs) (SA) and (HOMs) (ion) in the presence of W. [Display omitted] • In the process of autoxidation, the formation of an endoperoxide moiety in HOMs is not negligible. • During the formation of HOMs, the CO 2 elimination in presence of an unsaturated peroxy acyl radical is essential. • The formation and nucleation mechanisms of highly oxygenated organic molecules (HOMs) produced by limonene were investigated. • HOMs can self-aggregate into clusters and H 2 O molecules are beneficial to promote the NPF of HOMs in the presence of ions. [ABSTRACT FROM AUTHOR]

Ozonolysis of alkenes results in the formation of primary ozonides (POZs), which can subsequently decompose into carbonyl compounds and stabilized Criegee intermediates (sCIs). The sCIs generated from isoprene ozonolysis include the simplest congener, formaldehyde oxide (CH 2 OO), and isomers of C 4 -sCI. Although the bimolecular reaction with H 2 O is expected to be the main fate of sCIs, it was reported that sCIs can also react with carboxylic acids and/or organic hydroperoxides leading to gas-phase oligomeric compounds. While the impact of the gas-phase composition (H 2 O, sCI scavenger) on the formation of such products was recently studied, their fate remains unclear. In the present work, formation of oligomeric hydroperoxides from isoprene ozonolysis, proposed as reaction products composed of the sCI as a chain unit and formed from the insertion of sCI into a hydroperoxide or a carboxylic acid, was systematically examined in the presence of aerosol with varying compositions. The effect of hydroxyl (OH) radicals on the gas- and particle-phase compositions was investigated using diethyl ether as an OH radical scavenger. Thirty-four oligomeric compounds resulting from the insertion of sCIs into organic hydroperoxides or carboxylic acids were identified using iodide chemical ionization high-resolution mass spectrometry. Large reactive uptake onto acidified sulfate aerosol was observed for most of the characterized gaseous oligomeric species, whereas the presence of organic coatings and the lack of aerosol water significantly reduced or halted the reactive uptake of these species. These results indicate that highly oxidized molecules, such as hydroperoxides, could undergo multiphase reactions, which are significantly influenced by the chemical composition of seed aerosol. Furthermore, in addition to functionalization and accretion, decomposition and re-volatilization should be considered in SOA formation. [ABSTRACT FROM AUTHOR]

The NSLS-II storage ring is designed to operate with superconducting RF-cavities with the aim to store an average current of 500 mA distributed in 1080 bunches, with a gap in the uniform filling for ion clearing. At the early stage of the commissioning (phase 1), characterized by a bare lattice without damping wigglers and without Landau cavities, a normal conducting 7-cell PETRA-III RF-cavity structure has been installed with the goal to store an average current of 25 mA. In this paper we discuss our analysis of coupled-bunch instabilities driven by the Higher Order Modes (HOMs) of the 7-cell PETRA-III RF-cavity. As a cure of the instabilities, we apply a well-known scheme based on a proper detuning of the HOMs frequencies based upon cavity temperature change, and the use of the beneficial effect of the slow head–tail damping at positive chromaticity to increase the transverse coupled-bunch instability thresholds. In addition, we discuss measurements of coupled-bunch instabilities observed during the phase 1 commissioning of the NSLS-II storage ring. In our analysis we rely, in the longitudinal case, on the theory of coupled-bunch instability for uniform fillings, while in the transverse case we complement our studies with numerical simulations with OASIS , a novel parallel particle tracking code for self-consistent simulations of collective effects driven by short and long-range wakefields. [ABSTRACT FROM AUTHOR]

• Here, Ni/Co/Cu sulfide hollow multi-shell structure (NCCS-HoMS) with dodecahedral shape is developed. • A sequential templating approach with metal-organic frameworks, as a template was used. • NCCS-HoMS is demonstrated to be a superior electrode material for high-performance asymmetric SCs. • The obtained composite had an energy density above 87.5 Wh/Kg and a power density of 2807.6 W/kg. Supercapacitors (SCs) are ideal energy storage components because of their high-power density and long cycle life. Several properties of the electrode materials are required for high-performance SCs, including a large surface area, good conductivity, and a high level of stability. Herein, nickel/cobalt/copper sulfide hollow multi-shell structure (NCCS-HoMS) with dodecahedral shape is developed using a sequential templating approach (STA) with a metal-organic framework (MOF) as a template. The NCCS-HoMS, as superior electrode material in high-performance asymmetric SCs, exhibited good rate capability and cyclic stability (89.4% recovery after 5000 cycles) and an extremely high specific capacitance (2437.5 F/g). The synergistic effect of tri-metal structures provides better electrochemical performance than bimetallic or mono-metal oxides due to rich oxidation states and abundant active sites. The metal sulfide thin layers of the complex hollow structure with the high specific surface area increase the electroactive sites and mass transfer, supporting rapid reaction kinetics for solid samples. As a result, the NCCS-HoMS//AC asymmetric SC demonstrates a specific capacitance over 280 F/g at a current density of 1.0 A/g with an energy density above 87.5 [Display omitted] [ABSTRACT FROM AUTHOR]

Abstract: The main superconducting radio frequency (SRF) linacs of the international linear collider (ILC) operate at a frequency of 1.3GHz with a π phase advance per cell in the standing wave mode. An option being considered to reduce the overall footprint and project cost is to enhance the cavity gradient. The present baseline design for the main linacs of ILC demands the cavities to be able to reach a gradient of 35MV/m—although during commissioning and operation the gradient will be 31.5MV/m. This research concerns itself with the new cavity design with a view to reaching higher gradients. This design is focussed on minimising the surface electromagnetic fields and maximising the bandwidth of the accelerating mode. This new shape, which is referred to as the New Low Surface Field (NLSF) design. A design of a complete nine-cell cavity, including power couplers and higher order mode damping couplers is presented. [Copyright &y& Elsevier]

Abstract: The main travelling wave linacs of the compact linear collider (CLIC) operate at a frequency of 11.9942GHz with a phase advance per cell of 2π/3. In order to minimise the overall footprint of the accelerator, large accelerating gradients are sought. The present baseline design for the main linacs of CLIC demands an average electric field of 100MV/m. To achieve this in practical cavities entails the dual challenges of minimising the potential for electrical breakdown and ensuring the beam excited wakefield is sufficiently suppressed. We present a design to meet both of these conditions, together with a description of the structure, CLIC_DDS_A, expressively designed to experimentally test the ability of the structure to cope with high powers. [Copyright &y& Elsevier]

The reaction with chlorine radicals (·Cl) has been considered to be one of indispensable sinks for isoprene. However, the mechanism of ·Cl initiated isoprene reaction was not fully understood. Herein, the reaction of isoprene with ·Cl, and ensuing reactions of the resulting isoprene relevant radicals were investigated by combined quantum chemistry calculations and kinetics modeling. The results indicate that ·Cl addition to two terminal C-atoms of two double bonds of isoprene, forming IM 1 – 1 and IM 1 – 4 , are more favorable than H-abstractions from isoprene. Interestingly, the predicted reaction rate constant for the direct H-abstraction pathway is much lower than that of the indirect one, clarifying a direct H-abstraction mechanism for previously experimental observation. The IM 1 – 1 and IM 1 – 4 have distinct fate in their subsequent transformation. The reaction of IM 1 – 1 ends after the one-time O 2 addition. However, IM 1 – 4 can follow auto-oxidation mechanism with two times O 2 addition to finally form highly oxidized multi-functional molecules (HOMs), C 5 H 7 ClO 3 and ·OH. More importantly, the estimated contribution of ·Cl on HOMs (monomer only) formation from isoprene is lower than that of ·OH in addition pathway, implying overall HOMs yield from atmospheric isoprene oxidation could be overestimated if the role of ·Cl in transforming isoprene is ignored. Unlabelled Image • ·Cl addition to isoprene, forming IM 1 – 1 and IM 1 – 4 , is main pathway. • The direct H-abstraction of isoprene by ·Cl is the minor one. • The subsequent reaction of IM 1 – 1 ends after the one-time O 2 addition. • IM 1 – 4 further transform to form highly oxidized multi-functional molecules (HOMs). • ·Cl plays an essential role in estimating overall HOMs yield of isoprene oxidation. [ABSTRACT FROM AUTHOR]