Ion-Neutral Photofragment Coincidence Imaging of Photodissociation Dynamics of Ionic Species

The recently constructed cryogenic cylindrical ion trap velocity map imaging spectrometer (CIT-VMI) has been upgraded for coincidence imaging of both ionic and neutral photofragments from photodissociation of ionic species. The prepared ions are cooled down in a home-made cryogenic cylindrical ion trap and then extracted for photodissociation experiments. With the newly designed electric fields for extraction and acceleration, the ion beam can be accelerated to more than 4500 eV, which is necessary for velocity imaging of the neutral photofragments by using the position-sensitive imaging detector. The setup has been tested by the 355 nm photodissociation dynamics of the argon dimer cation (Ar\begin{document}$_2$\end{document}\begin{document}$^+$\end{document}). From the recorded experimental images of both neutral Ar and ionic Ar\begin{document}$^+$\end{document} fragments, we interpret velocity resolutions of \begin{document}$\Delta v/v$\end{document}\begin{document}$\approx$\end{document}4.6% for neutral fragments, and \begin{document}$\Delta v/v$\end{document}\begin{document}$\approx$\end{document}1.5% for ionic fragments, respectively.     

Photodissociation Dynamics of CS2 Near 204 nm: The S(3PJ)+CS(X1Σ+)Channels

We study the photodissociation dynamics of CS\begin{document}$_2$\end{document} in the ultraviolet region using the time-sliced velocity map ion imaging technique. The S(\begin{document}$^3$\end{document}P\begin{document}$_J$\end{document})+CS(\begin{document}$X^1\Sigma^+$\end{document}) product channels were observed and identified at four wavelengths of 201.36, 203.10, 204.85 and 206.61 nm. In the measured images of S(\begin{document}$^3$\end{document}P\begin{document}$_{J=2, 1, 0}$\end{document}), the vibrational states of the CS(\begin{document}$X^1\Sigma^+$\end{document}) co-products were partially resolved and the vibrational state distributions were determined. Moreover, the product total kinetic energy releases and the anisotropic parameters were derived. The relatively small anisotropic parameter values indicate that the S(\begin{document}$^3$\end{document}P\begin{document}$_{J=2, 1, 0}$\end{document})+CS(\begin{document}$X^1\Sigma^+$\end{document}) channels are very likely formed via the indirect predissociation process of CS\begin{document}$_2$\end{document}. The study of the S(\begin{document}$^3$\end{document}P\begin{document}$_{J=2, 1, 0}$\end{document})+CS(\begin{document}$X^1\Sigma^+$\end{document}) channels, which come from the spin-orbit coupling dissociation process of CS\begin{document}$_2$\end{document}, shows that nonadiabatic process plays a role in the ultraviolet photodissociation of CS\begin{document}$_2$\end{document}.     

Intra- and Intermolecular Rovibrational States of HCl-H\begin{document}$ _\textbf{2} $\end{document}O and DCl-H\begin{document}$ _\textbf{2} $\end{document}O Dimers from Full-Dimensional and Fully Coupled Quantum Calculations

We report full-dimensional and fully coupled quantum bound-state calculations of the \begin{document}$ J $\end{document} = 1 intra- and intermolecular rovibrational states of two isotopologues of the hydrogen chloride-water dimer, HCl-H\begin{document}$ _2 $\end{document}O (HH) and DCl-H\begin{document}$ _2 $\end{document}O (DH). The present study complements our recent theoretical investigations of the \begin{document}$ J $\end{document} = 0 nine-dimensional (9D) vibrational level structure of these and two other H/D isotopologues of this noncovalently bound molecular complex, and employs the same accurate 9D permutation invariant polynomial-neural network potential energy surface. The calculations yield all intramolecular vibrational fundamentals of the HH and DH dimers and the low-energy intermolecular rovibrational states in these intramolecular vibrational manifolds. The results are compared with those of the 9D \begin{document}$ J $\end{document} = 0 calculations of the same dimers. The energy differences between the \begin{document}$ K $\end{document} = 1 and \begin{document}$ K $\end{document} = 0 eigenstates exhibit pronounced variations with the intermolecular rovibrational states, for which a qualitative explanation is provided.     

One-Pot Synthesis of Tetraarylpyrrolo[3, 2-b]pyrrole Dopant-Free Hole-Transport Materials for Inverted Perovskite Solar Cells

Four organic small-molecule hole transport materials ( D41 , D42 , D43 and D44 ) of tetraarylpyrrolo[3, 2-b]pyrroles were prepared. They can be used without doping in the manufacture of the inverted planar perovskite solar cells. Tetraarylpyrrolo[3, 2-b]pyrroles are accessible for one-pot synthesis. D42 , D43 and D44 possess acceptor-\begin{document}$ \pi $\end{document}-donor-\begin{document}$ \pi $\end{document}-acceptor structure, on which the aryl bearing substitutes of cyan, fluorine and trifluoromethyl, respectively. Instead, the aryl moiety of D41 is in presence of methyl with a donor-\begin{document}$ \pi $\end{document}-donor-\begin{document}$ \pi $\end{document}-donor structure. The different substitutes significantly affected their molecular surface charge distribution and thin-film morphology, attributing to the electron-rich properties of fused pyrrole ring. The size of perovskite crystalline growth particles is affected by different molecular structures, and the electron-withdrawing cyan group of D42 is most conducive to the formation of large perovskite grains. The D42 fabricated devices with power conversion efficiency of 17.3% and retained 55% of the initial photoelectric conversion efficiency after 22 days in dark condition. The pyrrolo[3, 2-b]pyrrole is efficient electron-donating moiety for hole transporting materials to form good substrate in producing perovskite thin film.      

Impact of Zn(Ⅱ) Ions on Crystallization and Thermal Properties of Poly(lactic acid)

The issues of low crystallinity and slow crystallization rate of poly(lactic acid) (PLA) have been widely addressed. In this work, we find that doping PLA with Zn(Ⅱ) ions can speed up the process of crystallization of PLA. Three kinds of Zn(Ⅱ) salts (ZnCl\begin{document}$ _2 $\end{document}, ZnSt and ZnOAc) were tested in comparison with some other ions such as Mg(Ⅱ) and Ca(Ⅱ). The increased crystallinity and crystallization rate of PLA doping with Zn(Ⅱ) are reflected in FT-IR and variable temperature Raman spectroscopy. The crystallinity is further confirmed or measured with differential scanning calorimetry and X-ray diffraction. The crystallinity rate of the PLA/ZnSt-0.4 wt% material can reach 22.46% and the crystallinity rate of the PLA/ZnOAc-0.4 wt% material can reach 24.83%, as measured with differential scanning calorimetry.     

NH\begin{document}$ _\textbf{2} $\end{document}-MIL-53(Al) for Simultaneous Removal and Detection of Fluoride Anions

To address the limitations of the separate fluoride removal or detection in the existing materials, herein, amino-decorated metal organic frameworks NH\begin{document}$ _2 $\end{document}-MIL-53(Al) have been succinctly fabricated by a sol-hydrothermal method for simultaneous removal and determination of fluoride. As a consequence, the proposed NH\begin{document}$ _2 $\end{document}-MIL-53(Al) features high uptake capacity (202.5 mg/g) as well as fast adsorption rate, being capable of treating 5 ppm of fluoride solution to below the permitted threshold in drinking water within 15 min. Specifically, the specific binding between fluoride and NH\begin{document}$ _2 $\end{document}-MIL-53(Al) results in the release of fluorescent ligand NH\begin{document}$ _2 $\end{document}-BDC, conducive to the determination of fluoride via a concentration-dependent fluorescence enhancement effect. As expected, the resulting NH\begin{document}$ _2 $\end{document}-MIL-53(Al) sensor exhibits selective and sensitive detection (with the detection limit of 0.31 \begin{document}$ \mu $\end{document}mol/L) toward fluoride accompanied with a wide response interval (0.5-100 \begin{document}$ \mu $\end{document}mol/L). More importantly, the developed sensor can be utilized for fluoride detection in practical water systems with satisfying recoveries from 89.6% to 116.1%, confirming its feasibility in monitoring the practical fluoride-contaminated waters.      

\begin{document}$ \mathit{{Ab}} $\end{document} \begin{document}$ \mathit{{initio}} $\end{document} Molecular Dynamics Study of Adsorption of Hydroxyl Groups on Graphene Surface

Reduced graphene oxide is the precursor to produce graphene in a large scale; however, to date, there has been no consensus on the electronic structure of reduced graphene oxide. In this study, we carried out an \begin{document}$ ab $\end{document} \begin{document}$ initio $\end{document} molecular dynamics simulation to investigate the adsorption process of hydroxyl groups on graphene surface. During the adsorption process, the OH group needs to firstly pass through a physical adsorption complex with the OH above the bridge site of two carbon atoms, next to surmount a transition state, then to be adsorbed at the atop site of a carbon atom. With a 5\begin{document}$ \times $\end{document}5 graphene surface, up to 6 hydroxyl groups can be adsorbed on the graphene surface, indicating the concentration coverage of the hydroxyl groups on graphene surface is about 12%. The simulation results show that the negative adsorption energy increases linearly as the number of adsorbed hydroxyl groups increases, and the band gap also increases linearly with the number of adsorbed hydroxyl groups.     

Theoretical Investigating Mechanisms of Drug-Resistance Generated by Mutation-Induced Changes in Influenza Viruses

Influenza A (A/H\begin{document}$ x $\end{document}N\begin{document}$ y $\end{document}) is a significant public health concern due to its high infectiousness and mortality. Neuraminidase, which interacts with sialic acid (SIA) in host cells, has become an essential target since its highly conserved catalytic center structure, while resistance mutations have already generated. Here, a detailed investigation of the drug resistance mechanism caused by mutations was performed for subtype N9 (A/H7N9). Molecular dynamics simulation and alanine-scanning-interaction-entropy method (ASIE) were used to explore the critical differences between N9 and Zanamivir (ZMR) before and after R294K mutation. The results showed that the mutation caused the hydrogen bond between Arg294 and ZMR to break, then the hydrogen bonding network was disrupted, leading to weakened binding ability and resistance. While in wild type (A/H7N9\begin{document}$ ^{ \rm{WT}} $\end{document}), this hydrogen bond was initially stable. Meanwhile, N9 derived from A/H11N9 was obtained as an R292K mutation. Then the relative binding free energy of N9 with five inhibitors (SIA, DAN, ZMR, G28, and G39) was predicted, basically consistent with experimental values, indicating that the calculated results were reliable by ASIE. In addition, Arg292 and Tyr406 were hot spots in the A/H11N9\begin{document}$ ^{ \rm{WT}} $\end{document}-drugs. However, Lys292 was not observed as a favorable contributing residue in A/H11N9\begin{document}$ ^{ \rm{R292K}} $\end{document}, which may promote resistance. In comparison, Tyr406 remained the hotspot feature when SIA, ZMR, and G28 binding to A/H11N9\begin{document}$ ^{ \rm{R292K}} $\end{document}. Combining the two groups, we speculate that the resistance was mainly caused by the disruption of the hydrogen bonding network and the transformation of hotspots. This study could guide novel drug delivery of drug-resistant mutations in the treatment of A/H\begin{document}$ x $\end{document}N9.     

Ag-Cu Nanoparticles Supported on N-Doped TiO\begin{document}$_2$\end{document} Nanowire Arrays for Efficient Photocatalytic CO\begin{document}$_2$\end{document} Reduction

Photocatalytic reduction of CO\begin{document}$_2$\end{document} into various types of fuels has attracted great interest, and serves as a potential solution to addressing current global warming and energy challenges. In this work, Ag-Cu nanoparticles are densely supported on N-doped TiO\begin{document}$_2$\end{document} nanowire through a straightforward nanofabrication approach. The range of light absorption by N-doped TiO\begin{document}$_2$\end{document} can be tuned to match the plasmonic band of Ag nanoparticles, which allows synergizing a resonant energy transfer process with the Schottky junction. Meanwhile, Cu nanoparticles can provide active sites for the reduction of CO\begin{document}$_2$\end{document} molecules. Remarkably, the performance of photocatalytic CO\begin{document}$_2$\end{document} reduction is improved to produce CH\begin{document}$_4$\end{document} at a rate of 720 \begin{document}$\mu$\end{document}mol\begin{document}$\cdot$\end{document}g\begin{document}$^{-1}$\end{document}\begin{document}$\cdot$\end{document}h\begin{document}$^{-1}$\end{document} under full-spectrum irradiation.     

Theoretical Investigations on Photodissociation Dynamics of Deuterated Alkyl Halides CD3CH2F

The product branching ratio between different products in multichannel reactions is as important as the overall rate of reaction, both in terms of practical applications (\emph{e.g}. models of combustion or atmosphere chemistry) in understanding the fundamental mechanisms of such chemical reactions. A global ground state potential energy surface for the dissociation reaction of deuterated alkyl halide CD\begin{document}$ _3 $\end{document}CH\begin{document}$ _2 $\end{document}F was computed at the CCSD(T)/CBS//B3LYP/aug-cc-pVDZ level of theory for all species. The decomposition of CD\begin{document}$ _3 $\end{document}CH\begin{document}$ _2 $\end{document}F is controversial concerning C\begin{document}$ - $\end{document}F bond dissociation reaction and molecular (HF, DF, H\begin{document}$ _2 $\end{document}, D\begin{document}$ _2 $\end{document}, HD) elimination reaction. Rice-Ramsperger-Kassel-Marcus (RRKM) calculations were applied to compute the rate constants for individual reaction steps and the relative product branching ratios for the dissociation products were calculated using the steady-state approach. At the different energies studied, the RRKM method predicts that the main channel for DF or HF elimination from 1, 2-elimination of CD\begin{document}$ _3 $\end{document}CH\begin{document}$ _2 $\end{document}F is through a four-center transition state, whereas D\begin{document}$ _2 $\end{document} or H\begin{document}$ _2 $\end{document} elimination from 1, 1-elimination of CD\begin{document}$ _3 $\end{document}CH\begin{document}$ _2 $\end{document}F occurs through a direct three-center elimination. At 266, 248, and 193 nm photodissociation, the main product CD\begin{document}$ _2 $\end{document}CH\begin{document}$ _2 $\end{document}+DF branching ratios are computed to be 96.57%, 91.47%, and 48.52%, respectively; however, at 157 nm photodissociation, the product branching ratio is computed to be 16.11%. Based on these transition state structures and energies, the following photodissociation mechanisms are suggested: at 266, 248, 193 nm, CD\begin{document}$ _3 $\end{document}CH\begin{document}$ _2 $\end{document}F\begin{document}$ \rightarrow $\end{document}absorption of a photon\begin{document}$ \rightarrow $\end{document}TS5\begin{document}$ \rightarrow $\end{document}the formation of the major product CD\begin{document}$ _2 $\end{document}CH\begin{document}$ _2 $\end{document}+DF; at 157 nm, CD\begin{document}$ _3 $\end{document}CH\begin{document}$ _2 $\end{document}F\begin{document}$ \rightarrow $\end{document}absorption of a photon\begin{document}$ \rightarrow $\end{document}D/F interchange of TS1\begin{document}$ \rightarrow $\end{document}CDH\begin{document}$ _2 $\end{document}CDF\begin{document}$ \rightarrow $\end{document}H/F interchange of TS2\begin{document}$ \rightarrow $\end{document}CHD\begin{document}$ _2 $\end{document}CHDF\begin{document}$ \rightarrow $\end{document}the formation of the major product CHD\begin{document}$ _2 $\end{document}+CHDF.     

Enhanced Photovoltage for Inverted Perovskite Solar Cells Using Delafossite CuCrO2 Hole Transport Material

Poly(3, 4-ethylenedioxythiophene): poly(styrenesulfonate) (PEDOT: PSS) has been widely adopted as hole transport material (HTM) in inverted perovskite solar cells (PSCs), due to high optical transparency, good mechanical flexibility, and high thermal stability; however, its acidity and hygroscopicity inevitably hamper the long-term stability of the PSCs and its energy level does not match well with perovskite materials with a relatively low open-circuit voltage. In this work, p-type delafossite CuCrO\begin{document}$ _2 $\end{document} nanoparticles synthesized through hydrothermal method was employed as an alternative HTM for triple cation perovskite [(FAPbI\begin{document}$ _3 $\end{document})\begin{document}$ _{0.87} $\end{document}(MAPbBr\begin{document}$ _3 $\end{document})\begin{document}$ _{0.13} $\end{document}]\begin{document}$ _{0.92} $\end{document}(CsPbI\begin{document}$ _3 $\end{document})\begin{document}$ _{0.08} $\end{document} (possessing better photovoltaic performance and stability than conventional CH\begin{document}$ _3 $\end{document}NH\begin{document}$ _3 $\end{document}PbI\begin{document}$ _3 $\end{document}) based inverted PSCs. The average open-circuit voltage of PSCs increases from 908 mV of the devices with PEDOT: PSS HTM to 1020 mV of the devices with CuCrO\begin{document}$ _2 $\end{document} HTM. Ultraviolet photoemission spectroscopy demonstrates the energy band alignment between CuCrO\begin{document}$ _2 $\end{document} and perovskite is better than that between PEDOT: PSS and perovskite, the electrochemical impedance spectroscopy indicates CuCrO\begin{document}$ _2 $\end{document}-based PSCs exhibit larger recombination resistance and longer charge carrier lifetime than PEDOT: PSS-based PSCs, which contributes to the high \begin{document}$ V_{\rm{OC}} $\end{document} of CuCrO\begin{document}$ _2 $\end{document} HTM-based PSCs.     

Experimental and Theoretical Study on Dissociative Photoionization of Cyclopentanone

The dissociative photoionization of cyclopentanone was investigated by means of a reflectron time-of-flight mass spectrometer (RTOF-MS) with tunable vacuum ultraviolet synchrotron radiation in the photon energy range of 9.0-15.5 eV. The photoionization efficiency (PIE) curves for molecular ion and fragment ions were measured. The ionization energy of cyclopentanone was determined to be 9.23\begin{document}$\pm$\end{document}0.03 eV. Fragment ions from the dissociative photoionization of cyclopentanone were identified as C\begin{document}$_5$\end{document}H\begin{document}$_7$\end{document}O\begin{document}$^+$\end{document}, C\begin{document}$_4$\end{document}H\begin{document}$_5$\end{document}O\begin{document}$^+$\end{document}, C\begin{document}$_4$\end{document}H\begin{document}$_8^+$\end{document}/C\begin{document}$_3$\end{document}H\begin{document}$_4$\end{document}O\begin{document}$^+$\end{document}, C\begin{document}$_3$\end{document}H\begin{document}$_3$\end{document}O\begin{document}$^+$\end{document}, C\begin{document}$_4$\end{document}H\begin{document}$_6^+$\end{document}, C\begin{document}$_2$\end{document}H\begin{document}$_4$\end{document}O\begin{document}$^+$\end{document}, C\begin{document}$_3$\end{document}H\begin{document}$_6^+$\end{document}, C\begin{document}$_3$\end{document}H\begin{document}$_5^+$\end{document}, C\begin{document}$_3$\end{document}H\begin{document}$_4^+$\end{document}, C\begin{document}$_3$\end{document}H\begin{document}$_3^+$\end{document}, C\begin{document}$_2$\end{document}H\begin{document}$_5^+$\end{document} and C\begin{document}$_2$\end{document}H\begin{document}$_4^+$\end{document}. With the aid of the ab initio calculations at the \begin{document}$\omega$\end{document}B97X-D/6-31+G(d, p) level of theory, the dissociative mechanisms of C\begin{document}$_5$\end{document}H\begin{document}$_8$\end{document}O\begin{document}$^+$\end{document} are proposed. Ring opening and hydrogen migrations are the predominant processes in most of the fragmentation pathways of cyclopentanone.     

Reinvestigate the C2Π-X2Π(0,0) Band of AgO

The \begin{document}$ C^2\Pi $\end{document}-\begin{document}$ X^2\Pi $\end{document}(0, 0) band of AgO has been reinvestigated by laser induced fluorescence spectroscopy with a spectral resolution of \begin{document}$ \sim $\end{document}0.02 cm\begin{document}$ ^{-1} $\end{document}. The AgO molecules are produced by discharging a gas mixture of O\begin{document}$ _2 $\end{document}/Ar with silver needle electrodes in a supersonic jet expansion. By employing a home-made narrowband single longitude mode optical parametric oscillator (SLM-OPO) as the laser source, high-resolution spectra of the \begin{document}$ C^2\Pi $\end{document}-\begin{document}$ X^2\Pi $\end{document}(0, 0) band have been recorded for both \begin{document}$ ^{107} $\end{document}Ag\begin{document}$ ^{16} $\end{document}O and \begin{document}$ ^{109} $\end{document}Ag\begin{document}$ ^{16} $\end{document}O isotopologues. The spectroscopic constants of the \begin{document}$ C^2\Pi $\end{document} state are consequently determined, with the \begin{document}$ ^{109} $\end{document}Ag\begin{document}$ ^{16} $\end{document}O one being reported for the first time. The nature of the spin-orbit coupling effect in the \begin{document}$ C^2\Pi $\end{document} state is proposed to be due to state mixing with the nearby repulsive \begin{document}$ ^{4}\Sigma^{-} $\end{document} and \begin{document}$ ^{4}\Pi $\end{document} states.     

Bias-Polarity Dependent Electroluminescence from a Single Platinum Phthalocyanine Molecule

By using scanning tunneling microscope induced luminescence (STML) technique, we investigate systematically the bias-polarity dependent electroluminescence behavior of a single platinum phthalocyanine (PtPc) molecule and the electron excitation mechanisms behind. The molecule is found to emit light at both bias polarities but with different emission energies. At negative excitation bias, only the fluorescence at 637 nm is observed, which originates from the LUMO→HOMO transition of the neutral PtPc molecule and exhibits stepwise-like increase in emission intensities over three different excitation-voltage regions. Strong fluorescence in region (Ⅰ) is excited by the carrier injection mechanism with holes injected into the HOMO state first; moderate fluorescence in region (Ⅱ) is excited by the inelastic electron scattering mechanism; and weak fluorescence in region (Ⅲ) is associated with an up-conversion process and excited by a combined carrier injection and inelastic electron scattering mechanism involving a spin-triplet relay state. At positive excitation bias, more-than-one emission peaks are observed and the excitation and emission mechanisms become complicated. The sharp molecule-specific emission peak at ~911 nm is attributed to the anionic emission of PtPc\begin{document}$^-$\end{document} originated from the LUMO+1→LUMO transition, whose excitation is dominated by a carrier injection mechanism with electrons first injected into the LUMO+1 or higher-lying empty orbitals.     

Imaging Photodissociation Dynamics of MgO at 193 nm

In this work, we used time-sliced ion velocity imaging to study the photodissociation dynamics of MgO at \mbox{193 nm}. Three dissociation pathways are found through the speed and angular distributions of magnesium. One pathway is the one-photon excitation of MgO(X\begin{document}$^1\Sigma^+$\end{document}) to MgO(G\begin{document}$^1\Pi$\end{document}) followed by spin-orbit coupling between the G\begin{document}$^1\Pi$\end{document}, 3\begin{document}$^3\Pi$\end{document} and 1\begin{document}$^5\Pi$\end{document} states, and finally dissociated to the Mg(\begin{document}$^3$\end{document}P\begin{document}$_\textrm{u}$\end{document})+O(\begin{document}$^3$\end{document}P\begin{document}$_\textrm{g}$\end{document}) along the 1\begin{document}$^5\Pi$\end{document} surface. The other two pathways are one-photon absorption of MgO(A\begin{document}$^1\Pi$\end{document}) state to MgO(G\begin{document}$^1\Pi$\end{document}) and MgO(4\begin{document}$^1\Pi$\end{document}) state to dissociate into Mg(\begin{document}$^3$\end{document}P\begin{document}$_\textrm{u}$\end{document})+O(\begin{document}$^3$\end{document}P\begin{document}$_\textrm{g}$\end{document}) and Mg(\begin{document}$^1$\end{document}S\begin{document}$_\textrm{g}$\end{document})+O(\begin{document}$^1$\end{document}S\begin{document}$_\textrm{g}$\end{document}), respectively. The anisotropy parameters of the dissociation pathways are related to the lifetime of the vibrational energy levels and the coupling of rotational and vibronic spin-orbit states. The total kinetic energy analysis gives \begin{document}$D_0$\end{document}(Mg\begin{document}$-$\end{document}O)=21645\begin{document}$\pm$\end{document}50 cm\begin{document}$^{-1}$\end{document}.     

Theoretical Studies on Dihedral Angle-Bending Isomers of M2Pt20/-Clusters

The structures and electronic properties of the gaseous M\begin{document}$ _2 $\end{document}Pt\begin{document}$ _2 $\end{document}\begin{document}$ ^{0/-} $\end{document} clusters (M represents the alkaline earth metal) were investigated using the density functional theory (B3LYP and PBE0) and wave function theory (SCS-MP2, CCSD and CCSD (T)). The results indicate that the D\begin{document}$ _{2{h}} $\end{document} isomers with the planar structures are more stable than the C\begin{document}$ _{2v} $\end{document} isomers with smaller dihedral angles and shorter Pt-Pt bond lengths. The mutual competition of M(s, p)-Pt(5d) interaction and Pt-Pt covalent bonding contributes to the different stabilizations of the two kinds of isomers. The M(s, p)-Pt(5d) interaction favors the planar isomers with D\begin{document}$ _{2h} $\end{document} symmetry, while the Pt-Pt covalent bonding leads to the C\begin{document}$ _{2v} $\end{document} isomers with bending structures. Two different crossing points are determined in the potential energy curves of Be\begin{document}$ _2 $\end{document}Pt\begin{document}$ _2 $\end{document} with the singlet and triplet states. But there is just one crossing point in potential energy curves of Ra\begin{document}$ _2 $\end{document}Pt\begin{document}$ _2 $\end{document} and Ca\begin{document}$ _2 $\end{document}Pt\begin{document}$ _2 $\end{document}\begin{document}$ ^- $\end{document} because of flatter potential energy curves of Ra\begin{document}$ _2 $\end{document}Pt\begin{document}$ _2 $\end{document} with the triplet state or Ca\begin{document}$ _2 $\end{document}Pt\begin{document}$ _2 $\end{document}\begin{document}$ ^- $\end{document} with quartet state. The results reveal a unique example of dihedral angle-bending isomers with the smallest number of atoms and may help the understanding of the bonding properties of other potential angle-bending isomers.     

Electrosynthesis of Highly Efficient WO\begin{document}$_{3-x}$\end{document}/Graphene (Photo-)Electro- Catalyst by Two-Electrode Electrolysis System for Oxygen Evolution Reaction

Integration of non-noble transition metal oxides with graphene is known to construct high-activity electrocatalysts for oxygen evolution reduction (OER). In order to avoid the complexity of traditional synthesis process, a facile electrochemical method is elaborately designed to engineer efficient WO\begin{document}$_{3-x}$\end{document}/graphene (photo-)electrocatalyst for OER by a two-electrode electrolysis system, where graphite cathode is exfoliated into graphene and tungsten wire anode evolves into V\begin{document}$_\textrm{O}$\end{document}-rich WO\begin{document}$_{3-x}$\end{document} profiting from formed reductive electrolyte solution. Among as-prepared samples, WO\begin{document}$_{3-x}$\end{document}/G-2 shows the best electrocatalytic performance for OER with an overpotential of 320 mV (without iR compensation) at 10 mA/cm\begin{document}$^2$\end{document}, superior to commercial RuO\begin{document}$_2$\end{document} (341 mV). With introduction of light illumination, the activity of WO\begin{document}$_{3-x}$\end{document}/G-2 is greatly enhanced and its overpotential decreases to 290 mV, benefiting from additional reaction path produced by photocurrent effect and extra active sites generated by photogenerated carriers (h\begin{document}$^+$\end{document}). Characterization results indicate that both V\begin{document}$_\textrm{O}$\end{document}-rich WO\begin{document}$_{3-x}$\end{document} and graphene contribute to the efficient OER performance. The activity of WO\begin{document}$_{3-x}$\end{document} for OER is decided by the synergistic effect between V\begin{document}$_\textrm{O}$\end{document} concentration and particle size. The graphene could not only disperse WO\begin{document}$_{3-x}$\end{document} nanoparticles, but also improve the holistic conductivity and promote electron transmission. This work supports a novel method for engineering WO\begin{document}$_{3-x}$\end{document}/graphene composite for highly efficient (photo-)electrocatalytic performance for OER.     

Experimental and Theoretical Study on p-Chlorofluorobenzene in the S0, S1 and D0 States

The geometric structures and vibration frequencies of \begin{document}$ para $\end{document}-chlorofluorobenzene (\begin{document}$ p $\end{document}-ClFPh) in the first excited state of neutral and ground state of cation were investigated by resonance-enhanced multiphoton ionization and slow electron velocity-map imaging. The infrared spectrum of S\begin{document}$ _0 $\end{document} state and absorption spectrum for S\begin{document}$ _1 $\end{document}\begin{document}$ \leftarrow $\end{document}S\begin{document}$ _0 $\end{document} transition in \begin{document}$ p $\end{document}-ClFPh were also recorded. Based on the one-color resonant two-photon ionization spectrum and two-color resonant two-photon ionization spectrum, we obtained the adiabatic excited-state energy of \begin{document}$ p $\end{document}-ClFPh as 36302\begin{document}$ \pm $\end{document}4 cm\begin{document}$ ^{-1} $\end{document}. In the two-color resonant two-photon ionization slow electron velocity-map imagin spectra, the accurate adiabatic ionization potential of \begin{document}$ p $\end{document}-ClFPh was extrapolated as 72937\begin{document}$ \pm $\end{document}8 cm\begin{document}$ ^{-1} $\end{document} via threshold ionization measurement. In addition, Franck-Condon simulation was performed to help us confidently ascertain the main vibrational modes in the S\begin{document}$ _1 $\end{document} and D\begin{document}$ _0 $\end{document} states. Furthermore, the mixing of vibrational modes between S\begin{document}$ _0 $\end{document}\begin{document}$ \rightarrow $\end{document}S\begin{document}$ _1 $\end{document} and S\begin{document}$ _1 $\end{document}\begin{document}$ \rightarrow $\end{document}D\begin{document}$ _0 $\end{document} has been analyzed.     

Electronic Stability of Bimetallic Au2@Cu6 Nanocluster: Closed-Shell Interaction and Multicenter Bonding

Metallophilic interaction is a unique type of weak intermolecular interaction, where the electronic configuration of two metal atoms is closed shell. Despite its significance in multidisciplinary fields, the nature of metallophilic interaction is still not well understood. In this work, we investigated the electronic structures and bonding characteristic of bimetallic Au\begin{document}$ _{2} $\end{document}@Cu\begin{document}$ _{6} $\end{document} nanocluster through density functional theory method, which was reported in experiments recently [Angew. Chem. Int. Ed. 55 , 3611 (2016)]. In general thinking, interaction between two moieties of (CuSH)\begin{document}$ _{6} $\end{document} ring and (Au\begin{document}$ _{2} $\end{document}PH\begin{document}$ _{3} $\end{document})\begin{document}$ _{2} $\end{document} in the Au\begin{document}$ _{2} $\end{document}@Cu\begin{document}$ _{6} $\end{document} nanocluster can be viewed as a d\begin{document}$ ^{10} $\end{document}-\begin{document}$ \sigma $\end{document} closed-shell interaction. However, chemical bonding analysis shows that there is a ten center-two electron (10c-2e) multicenter bonding between two moieties. Further comparative studies on other bimetallic nanocluster M\begin{document}$ _{2} $\end{document}@Cu\begin{document}$ _{6} $\end{document} (M = Ag, Cu, Zn, Cd, Hg) also revealed that multicenter bonding is the origin of electronic stability of the complexes besides the d\begin{document}$ ^{10} $\end{document}-\begin{document}$ \sigma $\end{document} closed-shell interaction. This will provide valuable insights into the understanding of closed-shell interactions.     

Structures,Energetics, and Infrared Spectra of the Cationic Monomethylamine-Water Clusters

The structures, energetics, and infrared (IR) spectra of the cationic monomethylamine-water clusters, [(CH\begin{document}$_3$\end{document}NH\begin{document}$_2$\end{document})(H\begin{document}$_2$\end{document}O)\begin{document}$_n$\end{document}]\begin{document}$^+$\end{document} (\begin{document}$n$\end{document}=1\begin{document}$-$\end{document}5), have been studied using quantum chemical calculations at the MP2/6-311+G(2d,p) level. The results reveal that the formation of proton-transferred CH\begin{document}$_2$\end{document}NH\begin{document}$_3$\end{document}\begin{document}$^+$\end{document} ion core structure is preferred via the intramolecular proton transfer from the methyl group to the nitrogen atom and the water molecules act as the acceptor for the O\begin{document}$\cdots$\end{document}HN hydrogen bonds with the positively charged NH\begin{document}$_3$\end{document}\begin{document}$^+$\end{document} moiety of CH\begin{document}$_2$\end{document}NH\begin{document}$_3$\end{document}\begin{document}$^+$\end{document}, whose motif is retained in the larger clusters. The CH\begin{document}$_3$\end{document}NH\begin{document}$_2$\end{document}\begin{document}$^+$\end{document} ion core structure is predicted to be less energetically favorable. Vibrational frequencies of CH stretches, hydrogen-bonded and free NH stretches, and hydrogen-bonded OH stretches in the calculated IR spectra of the CH\begin{document}$_2$\end{document}NH\begin{document}$_3$\end{document}\begin{document}$^+$\end{document} and CH\begin{document}$_3$\end{document}NH\begin{document}$_2$\end{document}\begin{document}$^+$\end{document} type structures are different from each other, which would afford the sensitive probes for fundamental understanding of hydrogen bonding networks generated from the radiation-induced chemical processes in the [(CH\begin{document}$_3$\end{document}NH\begin{document}$_2$\end{document})(H\begin{document}$_2$\end{document}O)\begin{document}$_n$\end{document}]\begin{document}$^+$\end{document} complexes.