Conformations and Structures of Ethoxycarbonyl Isothiocyanate Revealed by Rotational Spectroscopy

The ethoxycarbonyl isothiocyanate has been investigated by using supersonic jet Fourier transform microwave spectroscopy. Two sets of rotational spectra belonging to conformers TCC (with the backbone of C\begin{document}$ - $\end{document}C\begin{document}$ - $\end{document}O\begin{document}$ - $\end{document}C, C\begin{document}$ - $\end{document}O\begin{document}$ - $\end{document}C=O, and O\begin{document}$ - $\end{document}C(=O)\begin{document}$ - $\end{document}NCS being trans, cis, and cis arranged, respectively) and GCC (\begin{document}$ gauche $\end{document}, cis, and cis arrangement of the C\begin{document}$ - $\end{document}C\begin{document}$ - $\end{document}O\begin{document}$ - $\end{document}C, C\begin{document}$ - $\end{document}O\begin{document}$ - $\end{document}C=O, and O\begin{document}$ - $\end{document}C(=O)\begin{document}$ - $\end{document}NCS) have been measured and assigned. The measurements of \begin{document}$ ^{13} $\end{document}C, \begin{document}$ ^{15} $\end{document}N and \begin{document}$ ^{34} $\end{document}S mono-substituted species of the two conformers have also been performed. The comprehensive rotational spectroscopic investigations provide accurate values of rotational constants and \begin{document}$ ^{14} $\end{document}N quadrupole coupling constants, which lead to structural determinations of the two conformers of ethoxycarbonyl isothiocyanate. For conformer TCC, the values of \begin{document}$ P_{ \rm{cc}} $\end{document} keep constant upon isotopic substitution, indicating that the heavy atoms of TCC are effectively located in the \begin{document}$ ab $\end{document} plane.     

Unravelling Hydrogen Adsorption Kinetics on Ir(111) Electrode in Acid Solutions by Impedance Spectroscopy

The kinetics for hydrogen (H) adsorption on Ir(111) electrode has been studied in both HClO\begin{document}$ _4 $\end{document} and H\begin{document}$ _2 $\end{document}SO\begin{document}$ _4 $\end{document} solutions by impedance spectroscopy. In HClO\begin{document}$ _4 $\end{document}, the adsorption rate for H adsorption on Ir(111) increases from 1.74\begin{document}$ \times $\end{document}10\begin{document}$ ^{-8} $\end{document} mol\begin{document}$ \cdot $\end{document}cm\begin{document}$ ^{-2} $\end{document}\begin{document}$ \cdot $\end{document}s\begin{document}$ ^{-1} $\end{document} to 3.47\begin{document}$ \times $\end{document}10\begin{document}$ ^{-7} $\end{document} mol\begin{document}$ \cdot $\end{document}cm\begin{document}$ ^{-2} $\end{document}\begin{document}$ \cdot $\end{document}s\begin{document}$ ^{-1} $\end{document} with the decrease of the applied potential from 0.2 V to 0.1 V (vs. RHE), which is ca. one to two orders of magnitude slower than that on Pt(111) under otherwise identical condition. This is explained by the stronger binding of water to Ir(111), which needs a higher barrier to reorient during the under potential deposition of H from hydronium within the hydrogen bonded water network. In H\begin{document}$ _2 $\end{document}SO\begin{document}$ _4 $\end{document}, the adsorption potential is ca. 200 mV negatively shifted, accompanied by a decrease of adsorption rate by up to one order of magnitude, which is explained by the hindrance of the strongly adsorbed sulfate/bisulfate on Ir(111). Our results demonstrate that under electrochemical environment, H adsorption is strongly affected by the accompanying displacement and reorientation of water molecules that initially stay close to the electrode surface.     

Photochemistry of Potassium Ferrocyanide and its Reaction with Uridine 5′-monophosphate in Aqueous Solution under Ultraviolet Irradiation

The photochemical reaction of potassium ferrocyanide (K\begin{document}$ _4 $\end{document}Fe(CN)\begin{document}$ _6 $\end{document}) exhibits excitation wavelength dependence and non-Kasha rule behavior. In this study, the excited-state dynamics of K\begin{document}$ _4 $\end{document}Fe(CN)\begin{document}$ _6 $\end{document} were studied by transient absorption spectroscopy. Excited state electron detachment (ESED) and photoaquation reactions were clarified by comparing the results of 260, 320, 340, and 350 nm excitations. ESED is the path to generate a hydrated electron (e\begin{document}$ _{\rm{aq}}^{-} $\end{document}). ESED energy barrier varies with the excited state, and it occurs even at the first singlet excited state (\begin{document}$ ^{1} $\end{document}T\begin{document}$ _{\rm{1g}} $\end{document}). The \begin{document}$ ^{1} $\end{document}T\begin{document}$ _{\rm{1g}} $\end{document} state shows \begin{document}$ {\sim} $\end{document}0.2 ps lifetime and converts into triplet [Fe(CN)\begin{document}$ _{6} $\end{document}]\begin{document}$ ^{4-} $\end{document} by intersystem crossing. Subsequently, \begin{document}$ ^{3} $\end{document}[Fe(CN)\begin{document}$ _{5} $\end{document}]\begin{document}$ ^{3-} $\end{document} appears after one CN\begin{document}$ ^{-} $\end{document} ligand is ejected. In sequence, H\begin{document}$ _{2} $\end{document}O attacks [Fe(CN)\begin{document}$ _{5} $\end{document}]\begin{document}$ ^{3-} $\end{document} to generate [Fe(CN)\begin{document}$ _{5} $\end{document}H\begin{document}$ _{2} $\end{document}O]\begin{document}$ ^{3-} $\end{document} with a time constant of approximately 20 ps. The \begin{document}$ ^{1} $\end{document}T\begin{document}$ _{\rm{1g}} $\end{document} state and e\begin{document}$ _{\rm{aq}}^{-} $\end{document} exhibit strong reducing power. The addition of uridine 5\begin{document}$ ' $\end{document}-monophosphate (UMP) to the K\begin{document}$ _{4} $\end{document}Fe(CN)\begin{document}$ _{6} $\end{document} solution decrease the yield of e\begin{document}$ _{\rm{aq}}^{-} $\end{document} and reduce the lifetimes of the e\begin{document}$ _{\rm{aq}}^{-} $\end{document} and \begin{document}$ ^{1} $\end{document}T\begin{document}$ _{\rm{1g}} $\end{document} state. The obtained reaction rate constant of \begin{document}$ ^{1} $\end{document}T\begin{document}$ _{\rm{1g}} $\end{document} state and UMP is 1.7\begin{document}$ {\times} $\end{document}10\begin{document}$ ^{14} $\end{document} (mol/L)\begin{document}$ ^{-1}\cdot $\end{document}s\begin{document}$ ^{-1} $\end{document}, and the e\begin{document}$ _{\rm{aq}}^{-} $\end{document} attachment to UMP is \begin{document}$ {\sim} $\end{document}8\begin{document}$ {\times} $\end{document}10\begin{document}$ ^{9} $\end{document} (mol/L)\begin{document}$ ^{-1}\cdot $\end{document}s\begin{document}$ ^{-1} $\end{document}. Our results indicate that the reductive damage of K\begin{document}$ _{4} $\end{document}Fe(CN)\begin{document}$ _{6} $\end{document} solution to nucleic acids under ultraviolet irradiation cannot be neglected.     

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.     

Doping Copper Ions in a Metal-Organic Framework (UiO-66-NH2):Location Effect Examined by Ultrafast Spectroscopy

We constructed two types of copper-doped metal-organic framework (MOF), i.e., Cu@UiO-66-NH\begin{document}$ _2 $\end{document} and Cu-UiO-66-NH\begin{document}$ _2 $\end{document}. In the former, Cu\begin{document}$ ^{2+} $\end{document} ions are impregnated in the pore space of the amine-functionalized, Zr-based UiO-66-NH\begin{document}$ _2 $\end{document}; while in the latter, Cu\begin{document}$ ^{2+} $\end{document} ions are incorporated to form a bimetal-center MOF, with Zr\begin{document}$ ^{4+} $\end{document} being partially replaced by Cu\begin{document}$ ^{2+} $\end{document} in the Zr\begin{document}$ - $\end{document}O oxo-clusters. Ultrafast spectroscopy revealed that the photoinduced relaxation kinetics associated with the ligand-to-cluster charge-transfer state is promoted for both Cu-doped MOFs relative to undoped one, but in a sequence of Cu-UiO-66-NH\begin{document}$ _2 $\end{document}\begin{document}$ > $\end{document}Cu@UiO-66-NH\begin{document}$ _2 $\end{document}\begin{document}$ > $\end{document}UiO-66-NH\begin{document}$ _2 $\end{document}. Such a sequence turned to be in line with the trend observed in the visible-light photocatalytic hydrogen evolution activity tests on the three MOFs. These findings highlighted the subtle effect of copper-doping location in this Zr-based MOF system, further suggesting that rational engineering of the specific metal-doping location in alike MOF systems to promote the photoinduced charge separation and hence suppress the detrimental charge recombination therein is beneficial for achieving improved performances in MOF-based photocatalysis.     

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.     

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.     

GW/BSE Nonadiabatic Dynamics Simulations on Excited-State Relaxation Processes of Zinc Phthalocyanine-Fullerene Dyads: Roles of Bridging Chemical Bonds

In this work, we employ electronic structure calculations and nonadiabatic dynamics simulations based on many-body Green function and Bethe-Salpeter equation (GW/BSE) methods to study excited-state properties of a zinc phthalocyanine-fullerene (ZnPc-C\begin{document}$ _{60} $\end{document}) dyad with 6-6 and 5-6 configurations. In the former, the initially populated locally excited (LE) state of ZnPc is the lowest S\begin{document}$ _1 $\end{document} state and thus, its subsequent charge separation is relatively slow. In contrast, in the latter, the S\begin{document}$ _1 $\end{document} state is the LE state of C\begin{document}$ _{60} $\end{document} while the LE state of ZnPc is much higher in energy. There also exist several charge-transfer (CT) states between the LE states of ZnPc and C\begin{document}$ _{60} $\end{document}. Thus, one can see apparent charge separation dynamics during excited-state relaxation dynamics from the LE state of ZnPc to that of C\begin{document}$ _{60} $\end{document}. These points are verified in dynamics simulations. In the first 200 fs, there is a rapid excitation energy transfer from ZnPc to C\begin{document}$ _{60} $\end{document}, followed by an ultrafast charge separation to form a CT intermediate state. This process is mainly driven by hole transfer from C\begin{document}$ _{60} $\end{document} to ZnPc. The present work demonstrates that different bonding patterns (i.e. 5-6 and 6-6) of the C\begin{document}$ - $\end{document}N linker can be used to tune excited-state properties and thereto optoelectronic properties of covalently bonded ZnPc-C\begin{document}$ _{60} $\end{document} dyads. Methodologically, it is proven that combined GW/BSE nonadiabatic dynamics method is a practical and reliable tool for exploring photoinduced dynamics of nonperiodic dyads, organometallic molecules, quantum dots, nanoclusters, etc.     

Structural Dynamics of Amyloid β Peptide Binding to Acetylcholine Receptor and Virtual Screening for Effective Inhibitors

The interaction between Amyloid β (Aβ) peptide and acetylcholine receptor is the key for our understanding of how Aβ fragments block the ion channels within the synapses and thus induce Alzheimer's disease. Here, molecular docking and molecular dynamics (MD) simulations were performed for the structural dynamics of the docking complex consisting of Aβ and α7-nAChR (α7 nicotinic acetylcholine receptor), and the inter-molecular interactions between ligand and receptor were revealed. The results show that A\begin{document}$ \beta_{25-35} $\end{document} is bound to α7-nAChR through hydrogen bonds and complementary shape, and the A\begin{document}$ \beta_{25-35} $\end{document} fragments would easily assemble in the ion channel of \begin{document}$ \alpha $\end{document}7-nAChR, then block the ion transfer process and induce neuronal apoptosis. The simulated amide-I band of A\begin{document}$ \beta_{25-35} $\end{document} in the complex is located at 1650.5 cm\begin{document}$ ^{-1} $\end{document}, indicating the backbone of A\begin{document}$ \beta_{25-35} $\end{document} tends to present random coil conformation, which is consistent with the result obtained from cluster analysis. Currently existing drugs were used as templates for virtual screening, eight new drugs were designed and semi-flexible docking was performed for their performance. The results show that, the interactions between new drugs and \begin{document}$ \alpha $\end{document}7-nAChR are strong enough to inhibit the aggregation of A\begin{document}$ \beta_{25-35} $\end{document} fragments in the ion channel, and also be of great potential in the treatment of Alzheimer's disease.     

Designer Mg-Mg and Zn-Zn Single Bonds Facilitated by Double Aromaticity in the M2B7-(M=Mg,Zn) Clusters

The simple homodinuclear M

\begin{document}$ - $\end{document}

M single bonds for group II and XII elements are difficult to obtain as a result of the fulfilled s

\begin{document}$ ^2 $\end{document}

electronic configurations, consequently, a dicationic prototype is often utilized to design the M

\begin{document}$ ^+ $\end{document}\begin{document}$ - $\end{document}

M

\begin{document}$ ^+ $\end{document}

single bond. Existing studies generally use sterically bulky organic ligands L

\begin{document}$ ^- $\end{document}

to synthesize the compounds in the L

\begin{document}$ ^- $\end{document}\begin{document}$ - $\end{document}

M

\begin{document}$ ^+ $\end{document}\begin{document}$ - $\end{document}

M

\begin{document}$ ^+ $\end{document}\begin{document}$ - $\end{document}

L

\begin{document}$ ^- $\end{document}

manner. However, here we report the design of Mg

\begin{document}$ - $\end{document}

Mg and Zn

\begin{document}$ - $\end{document}

Zn single bonds in two ligandless clusters, Mg

\begin{document}$ _2 $\end{document}

B

\begin{document}$ _7 $\end{document}\begin{document}$ ^- $\end{document}

and Zn

\begin{document}$ _2 $\end{document}

B

\begin{document}$ _7 $\end{document}\begin{document}$ ^- $\end{document}

, using density functional theory methods. The global minima of both of the clusters are in the form of M

\begin{document}$ _2 $\end{document}\begin{document}$ ^{2+} $\end{document}

(B

\begin{document}$ _7 $\end{document}\begin{document}$ ^{3-} $\end{document}

), where the M

\begin{document}$ - $\end{document}

M single bonds are positioned above a quasi-planar hexagonal B

\begin{document}$ _7 $\end{document}

moiety. Chemical bonding analyses further confirm the existence of Mg

\begin{document}$ - $\end{document}

Mg and Zn

\begin{document}$ - $\end{document}

Zn single bonds in these clusters, which are driven by the unusually stable B

\begin{document}$ _7 $\end{document}\begin{document}$ ^{3-} $\end{document}

moiety that is both

\begin{document}$ \sigma $\end{document}

and

\begin{document}$ \pi $\end{document}

aromatic. Vertical detachment energies of Mg

\begin{document}$ _2 $\end{document}

B

\begin{document}$ _7 $\end{document}\begin{document}$ ^- $\end{document}

and Zn

\begin{document}$ _2 $\end{document}

B

\begin{document}$ _7 $\end{document}\begin{document}$ ^- $\end{document}

are calculated to be 2.79 eV and 2.94 eV, respectively, for the future comparisons with experimental data.

     

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.     

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.     

Insights into Syngas to Methanol Conversion on Cr2O3 Oxide from First-Principles-based Microkinetic Simulations

Cr\begin{document}$ _2 $\end{document}O\begin{document}$ _3 $\end{document} has been recognized as a key oxide component in bifunctional catalysts to produce bridging intermediate, e.g., methanol, from syngas. By combining density functional theory calculations and microkinetic modeling, we computationally studied the surface structures and catalytic activities of bare Cr\begin{document}$ _2 $\end{document}O\begin{document}$ _3 $\end{document} (001) and (012) surfaces, and two reduced (012) surfaces covered with dissociative hydrogens or oxygen vacancies. The reduction of (001) surface is much more difficult than that of (012) surface. The stepwise or the concerted reaction pathways were explored for the syngas to methanol conversion, and the hydrogenation of CO or CHO is identified as rate-determining step. Microkinetic modeling reveals that (001) surface is inactive for the reaction, and the rates of both reduced (012) surfaces (25-28 s\begin{document}$ ^{-1} $\end{document}) are about five times higher than bare (012) surface (4.3 s\begin{document}$ ^{-1} $\end{document}) at 673 K. These theoretical results highlight the importance of surface reducibility on the reaction and may provide some implications on the design of individual component in bifunctional catalysis.     

Microwave Spectrum and Structure of 2-(Trifluoromethyl)pyridine

The high resolution rotational spectrum of 2-(trifluoromethyl)pyridine in 2\begin{document}$ - $\end{document}20 GHz was recorded and analyzed. Spectroscopic parameters including rotational constants, nuclear quadrupole coupling constants of \begin{document}$ ^{14} $\end{document}N as well as the centrifugal distortion constants were determined. The rotational spectra of five mono-substituted \begin{document}$ ^{13} $\end{document}C and one \begin{document}$ ^{15} $\end{document}N isotopologues were also measured and assigned in natural abundance. Experimental results complemented by ab initio calculations lead to an accurate determination of the skeleton structure. The values of the planar moment inertia \begin{document}$ P_{cc} $\end{document} were determined to be 44.46 u?\begin{document}$ ^2 $\end{document} for all the measured isotopologues, indicating a C\begin{document}$ _ \rm{s} $\end{document} symmetry of this molecule. The molecular electrostatic surface potential was calculated to illustrate the trifluoromethyl substitution effects on the electron distribution.     

Low-Lying Isomers of (TiO\begin{document}$_{2}$\end{document})\begin{document}$_{n}$\end{document} (\begin{document}${n}$\end{document}=2-8) Clusters

Although there are diverse bond features of Ti and O atoms, so far only several isomers have been reported for each (TiO\begin{document}$_2$\end{document})\begin{document}$_n$\end{document} cluster. Instead of the widely used global optimization, in this work, we search for the low-lying isomers of (TiO\begin{document}$_2$\end{document})\begin{document}$_n$\end{document} (\begin{document}$n$\end{document}=2\begin{document}$-$\end{document}8) clusters with up to 10000 random sampling initial structures. These structures were optimized by the PM6 method, followed by density functional theory calculations. With this strategy, we have located many more low-lying isomers than those reported previously. The number of isomers increases dramatically with the size of the cluster, and about 50 isomers were found for (TiO\begin{document}$_2$\end{document})\begin{document}$_7$\end{document} and (TiO\begin{document}$_2$\end{document})\begin{document}$_8$\end{document} with the energy within kcal/mol. Furthermore, new lowest isomers have been located for (TiO\begin{document}$_2$\end{document})\begin{document}$_5$\end{document} and (TiO\begin{document}$_2$\end{document})\begin{document}$_8$\end{document}, and isomers with three terminal oxygen atoms, five coordinated oxygen atoms as well as six coordinated titanium atoms have been located. Our work highlights the diverse structural features and a large number of isomers of small TiO\begin{document}$_2$\end{document} clusters.     

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.     

Effect of a Single Repeat Sequence of the Human Telomere d(TTAGGG) on Structure of Single-Stranded Telomeric DNA d[AGGG(TTAGGG)\begin{document}$_6$\end{document}]

The structures of human telomeric DNA have received much attention due to its significant biological importance. Most studies have focused on G-quadruplex structure formed by short telomeric DNA sequence, but little is known about the structures of long single-stranded telomeric DNAs. Here, we investigated the structure of DNA with a long sequence of d[AGGG(TTAGGG)\begin{document}$_6$\end{document}] (G\begin{document}$_6$\end{document}-DNA) and the effect of a single repeat sequence d(TTAGGG) (G\begin{document}$_{01}$\end{document}-DNA) on the structure of G\begin{document}$_6$\end{document}-DNA using sedimentation velocity technique, polyacrylamide gel electrophoresis, circular dichroism spectroscopy, and UV melting experiments. The results suggest that the G\begin{document}$_6$\end{document}-DNA can form dimers in aqueous solutions and G\begin{document}$_{01}$\end{document}-DNA can form additional G-quadruplex structures by binding to G\begin{document}$_6$\end{document}-DNA. However, G\begin{document}$_{01}$\end{document}-DNA has no effect on the structure of DNA with a sequence of d[AGGG(TTAGGG)\begin{document}$_3$\end{document}] (G\begin{document}$_3$\end{document}-DNA). Our study provides new insights into the structure polymorphism of long human single-stranded telomeric DNA.     

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.     

Effect of Optical Depth on Study of Chemical Properties of Massive Star Forming Clumps

Here we present the study on chemical properties of massive star forming clumps using N\begin{document}$ _2 $\end{document}H\begin{document}$ ^+ $\end{document}(1-0), H\begin{document}$ ^{13} $\end{document}CO\begin{document}$ ^+ $\end{document}(1-0), HCN(1-0) and HN\begin{document}$ ^{13} $\end{document}C(1-0) data from the literature [Astron. Astrophys. 563 , A97 (2014)]. We found that abundances of H\begin{document}$ ^{13} $\end{document}CO\begin{document}$ ^+ $\end{document} and HN\begin{document}$ ^{13} $\end{document}C are affected by H\begin{document}$ _2 $\end{document} column densities. As the median values of these two abundances increase by nearly 10 times from stages A to B, H\begin{document}$ ^{13} $\end{document}CO\begin{document}$ ^+ $\end{document} and HN\begin{document}$ ^{13} $\end{document}C are suitable for tracing the evolution of massive star forming clumps. The order of rapidity in growth of abundances of all the four studied molecules from stages A to B, is H\begin{document}$ ^{13} $\end{document}CO\begin{document}$ ^+ $\end{document}, HCN, HN\begin{document}$ ^{13} $\end{document}C, and N\begin{document}$ _2 $\end{document}H\begin{document}$ ^+ $\end{document}, from the highest to the lowest. Our results suggest that the observing optically thin molecular lines with high angular resolution are necessary to study the chemical evolution of massive star forming clumps.     

Gamma Ray Radiation Effect on \begin{document}$\rm{{Bi}}_{2}$\end{document}W\begin{document}$\rm{{O}}_{6}$\end{document} Photocatalyst

The development of \begin{document}$\rm{Bi}_2$\end{document}W\begin{document}$\rm{O}_6$\end{document}-based materials has become one of research hotspots due to the increasing demands on high-efficient photocatalyst responding to visible light. In this work, the effect of high energy radiation (\begin{document}$\gamma$\end{document}-ray) on the structure and the photocatalytic activity of \begin{document}$\rm{Bi}_2$\end{document}W\begin{document}$\rm{O}_6$\end{document} nanocrystals was first studied. No morphological change of \begin{document}$\rm{Bi}_2$\end{document}W\begin{document}$\rm{O}_6$\end{document} nanocrystals was observed by SEM under \begin{document}$\gamma$\end{document}-ray radiation. However, the XRD spectra of the irradiated \begin{document}$\rm{Bi}_2$\end{document}W\begin{document}$\rm{O}_6$\end{document} nanocrystals showed the characteristic 2\begin{document}$\theta$\end{document} of (113) plane shifts slightly from 28.37\begin{document}$^{\rm{o}}$\end{document} to 28.45\begin{document}$^{\rm{o}}$\end{document} with the increase of the absorbed dose, confirming the change in the crystal structure of \begin{document}$\rm{Bi}_2$\end{document}W\begin{document}$\rm{O}_6$\end{document}. The XPS results proved the crystal structure change was originated from the generation of oxygen vacancy defects under high-dose radiation. The photocatalytic activity of \begin{document}$\rm{Bi}_2$\end{document}W\begin{document}$\rm{O}_6$\end{document} on the decomposition of methylene blue (MB) in water under visible light increases gradually with the increase of absorbed dose. Moreover, the improved photocatalytic performance of the irradiated \begin{document}$\rm{Bi}_2$\end{document}W\begin{document}$\rm{O}_6$\end{document} nanocrystals remained after three cycles of photocatalysis, indicating a good stability of the created oxygen vacancy defects. This work gives a new simple way to improve photocatalytic performance of \begin{document}$\rm{Bi}_2$\end{document}W\begin{document}$\rm{O}_6$\end{document} through creating oxygen vacancy defects in the crystal structure by \begin{document}$\gamma$\end{document}-ray radiation.