Yanbo Gai

Structure, stability, and electronic property of carbon-doped gold clusters AunC− (n = 1–10): A density functional theory study

The equilibrium geometric structures, relative stabilities, and electronic properties of Au(n)C(-) and Au(n+1)(-) (n = 1-10) clusters are systematically investigated using density functional theory with hyper-generalized gradient approximation. The optimized geometries show that one Au atom capped on Au(n-1)C(-) clusters is a dominant growth pattern for Au(n)C(-) clusters. In contrast to Au(n+1)(-) clusters, Au(n)C(-) clusters are most stable in a quasi-planar or three-dimensional structure because C doping induces the local non-planarity while the rest of the structure continues to grow in a planar mode, resulting in an overall non-2D configuration. The relative stability calculations show that the impurity C atom can significantly enhance the thermodynamic stability of pure gold clusters. Moreover, the effect of C atom on the Au(n)(-) host decreases with the increase of cluster size. The HOMO-LUMO gap curves show that the interaction of the C atom with Au(n)(-) clusters improves the chemical stability of pure gold clusters, except for Au3(-) and Au4(-) clusters. In addition, a natural population analysis shows that the charges in corresponding Au(n)C(-) clusters transfer from the Au(n)(-) host to the C atom. Meanwhile, a natural electronic configuration analysis also shows that the charges mainly transfer between the 2s and 2p orbitals within the C atom.

A density functional study of phosphorus-doped gold clusters: AunP− (n = 1–8)

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.

Theoretical studies of the hydration reactions of stabilized Criegee intermediates from the ozonolysis of β-pinene

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.

Ultra-sensitive measurement of peroxy radicals by chemical amplification broadband cavity-enhanced spectroscopy

The PERCA (PEroxy Radical Chemical Amplification) technique, which is based on the catalytic conversion of ambient peroxy radicals (HO2 and RO2, where R stands for any organic chain) to a larger amount of nitrogen dioxide (NO2) amplified by chain reactions by adding high concentrations of NO and CO in the flow reactor, has been widely used for total peroxy radical RO2* (RO2* = HO2 + ΣRO2) measurements. High-sensitivity and accurate measurement of the NO2 concentration plays a key role in accurate measurement of the RO2* concentration. In this paper, we report on the development of a dual-channel chemical amplification instrument, which combined the PERCA method with the incoherent broadband cavity-enhanced absorption spectroscopy (IBBCEAS), for peroxy radical measurements. The IBBCEAS method is capable of simultaneously measuring multiple species with high spectral identification, and can directly measure NO2 concentrations with high sensitivity and high accuracy and without interference from other absorbers. The detection sensitivity of the developed PERCA-IBBCEAS instrument for HO2 radicals was estimated to be about 0.9 pptv (1σ, 60 s) at a relative humidity (RH) of 10%. Considering the error sources of NO2 detection, CL determination, and the radical partitioning in the air sample, the total uncertainty of RO2* measurements was about 16-20%.

Experimental and Theoretical Study of Reactions of OH Radicals with Hexenols: An Evaluation of the Relative Importance of the H-Abstraction Reaction Channel.

C6 hexenols are one of the most significant groups of volatile organic compounds with biogenic emissions. The lack of corresponding kinetic parameters and product information on their oxidation reactions will result in incomplete atmospheric chemical mechanisms and models. In this paper, experimental and theoretical studies are reported for the reactions of OH radicals with a series of C6 hexenols, (Z)-2-hexen-1-ol, (Z)-3-hexen-1-ol, (Z)-4-hexen-1-ol, (E)-2-hexen-1-ol, (E)-3-hexen-1-ol, and (E)-4-hexen-1-ol, at 298 K and 1.01 × 10(5) Pa. The corresponding rate constants were 8.53 ± 1.36, 10.1 ± 1.6, 7.86 ± 1.30, 8.08 ± 1.33, 9.10 ± 1.50, and 7.14 ± 1.20 (in units of 10(-11) cm(3) molecule(-1) s(-1)), respectively, measured by gas chromatography with a flame ionization detector (GC-FID), using a relative technique. Theoretical calculations concerning the OH-addition and H-abstraction reaction channels were also performed for these reactions to further understand the reaction mechanism and the relative importance of the H-abstraction reaction. By contrast to previously reported results, the H-abstraction channel is a non-negligible reaction channel for reactions of OH radicals with these hexenols. The rate constants of the H-abstraction channel are comparable with those for the OH-addition channel and contribute >20% for most of the studied alcohols, even >50% for (E)-3-hexen-1-ol. Thus, H-abstraction channels may have an important role in the reactions of these alcohols with OH radicals and must be considered in certain atmospheric chemical mechanisms and models.

Three-Dimensional Assignment of the Structures of Atomic Clusters: an Example of Au8M (M=Si, Ge, Sn) Anion Clusters

Identification of different isomer structures of atomic and molecular clusters has long been a challenging task in the field of cluster science. Here we present a three-dimensional (3D) assignment method, combining the energy (1D) and simulated (2D) spectra to assure the assignment of the global minimum structure. This method is more accurate and convenient than traditional methods, which only consider the total energy and first vertical detachment energies (VDEs) of anion clusters. There are two prerequisites when the 3D assignment method is ultilized. First, a reliable global minimum search algorithm is necessary to explore enough valleys on the potential energy surface. Second, trustworthy simulated spectra are necessary, that is to say, spectra that are in quantitative agreement. In this paper, we demonstrate the validity of the 3D assignment method using Au8M− (M = Si, Ge, Sn) systems. Results from this study indicate that the global minimum structures of Au8Ge− and Au8Sn− clusters are different from those described in previous studies.

A Smog Chamber Facility for Qualitative and Quantitative Study on Atmospheric Chemistry and Secondary Organic Aerosol

In order to investigate the atmospheric oxidation processes and the formation of secondary organic aerosol (SOA), an indoor environmental reaction smog chamber are constructed and characterized. The system consists of the collapsible ∼830 L FEP Teflon film main reactor, in which the atmospheric chemical reactions take place and the formation of SOA occurs under the simulated atmospheric conditions, and the diverse on-line gas- and particle-phase instrumentation, such as the proton transfer reaction mass spectrometer, the synchrotron radiation photoionization mass spectrometer, the aerosol laser time-of-flight mass spectrometer, and other traditional commercial instruments. The initial characterization experiments are described, concerning the temperature and ultraviolet light intensity, the reactivity of the pure air, the wall loss rates of gaseous compounds and particulate matter. And the initial evaluation experiments for SOA yields from the ozonolysis of α-pinene and for mass spectra of the products re...

Kinetic and mechanistic study on gas phase reactions of ozone with a series of cis-3-hexenyl esters

As an important group of green leaf volatiles (GLVs), C6 hexenyl esters, are found to be widely emitted into the atmosphere by plants and vegetation, especially when they suffer mechanical damage. It is indispensable to understand their atmospheric fate for environmental assessment and model simulation. In this paper, the rate constants for reactions of O3 with four cis-3-hexenyl esters have been measured using an absolute method in a flow tube reactor at 298 K and atmospheric pressure. The measured rate constants (in 10−17 cm3 per molecule per s) were 4.06 ± 0.66 for cis-3-hexenyl formate, 5.77 ± 0.70 for cis-3-hexenyl acetate, 7.62 ± 0.88 for cis-3-hexenyl propionate, and 12.34 ± 1.59 for cis-3-hexenyl butyrate, respectively. Theoretical calculations were also carried out for the title reactions to better understand their kinetics and mechanism using density functional theory (DFT) and transition state theory (TST). Geometry optimizations, energy and harmonic vibrational frequency calculations were performed for all of the stationary points at the BHandHLYP/6-311+G(d,p) level of theory. The calculated rate constants were in good agreement with the experimental values. The results showed that the reactivity of the studied compounds towards O3 was obviously dependent on their chemical structure, such as the nature of the substituent, and the relative positions of the double bond and the substituent. The results were also discussed in terms of their atmospheric importance in the degradation of these unsaturated esters by comparing their lifetimes with respect to their reactions with O3 and other main atmospheric oxidants.

VUV photoionization aerosol mass spectrometric study on the iodine oxide particles formed from O3-initiated photooxidation of diiodomethane (CH2I2)

Iodine oxide particles (IOPs) formed from O3-initiated photooxidation of diiodomethane have been investigated based on the combination of a thermal desorption/tunable vacuum ultraviolet time-of-flight photoionization aerosol mass spectrometer (TD-VUV-TOF-PIAMS) with a flow reactor for the first time. Characterization of the home-made flow reactor was performed, which indicates the applicability of its combination with TD-VUV-TOF-PIAMS. Based on that, aerosol mass spectra of IOP formation from photooxidation of CH2I2/O3 were studied on-line taking full advantage of both the virtues of the flow reactor and TD-VUV-TOF-PIAMS. The main chemical components of IOPs, including atomic and molecular iodine (I, I2), iodine oxides (IO, OIO, I2O and I2O3) and hydrogen-containing iodine species (HI, HIO and HIO3), were observed and identified based on the corresponding photoionization energy (PIE) curves, and the probable chemical composition and formation mechanism of IOPs were proposed. The work has not only improved the understanding of the formation mechanism of IOPs, but also demonstrated the capability of TD-VUV-TOF-PIAMS for direct molecular characterization of aerosols in flow reactor experiments, whose potential application in mass spectrometric studies of atmospheric aerosols is anticipated.

Kinetics and mechanisms of gas phase reactions of hexenols with ozone

An absolute kinetic study is reported for the reactions of O3 with a series of C6 hexenols, (Z)-2-hexen-1-ol, (Z)-3-hexen-1-ol, (Z)-4-hexen-1-ol, (E)-2-hexen-1-ol, (E)-3-hexen-1-ol, and (E)-4-hexen-1-ol. At 298 K and atmospheric pressure, the rate constants (in units of 10−17 cm3 molecule−1 s−1) were measured to be 7.44 ± 1.03, 5.47 ± 0.71, 7.09 ± 0.91, 16.6 ± 2.2, 6.19 ± 0.72 and 10.5 ± 1.4, respectively. To gain a deeper insight into the reactivity and mechanism, theoretical calculations were also performed for the title reactions with the methods of density functional theory (DFT) and transition-state theory (TST). The geometries, energies, and harmonic vibrational frequencies of each stationary point were obtained at the BH&HLYP/6-31+G(d,p) level of theory. The calculated rate constants are in good agreement with the experimental data, and the reactivity of hexenols with O3 shows a strong dependence on their chemical structure based on the theoretical results. Finally, lifetimes of the C6 hexenols, with respect to their reactions with some important atmospheric oxidants such as O3, OH and NO3 radicals, have also been discussed in the article.