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The product branching ratio between different products in multichannel reactions is as important as the over-all rate of reaction, both in terms of practical applications ( 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 CD3CH2F was computed at the CCSD(T)/CBS//B3LYP/aug-cc-pVDZ level of theory for all species. The decomposition of CD3CH2F is controversial concerning C−F bond dissociation reaction and molecular (HF, DF, H2, D2, 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 CD3CH2F is through a four-center transition state, whereas D2 or H2 elimination from 1,1-elimination of CD3CH2F occurs through a direct three-center elimination. At 266, 248, and 193 nm photodissociation, the main product CD2CH2+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, CD3CH2F→absorption of a photon→TS5→the formation of the major product CD2CH2+DF; at 157 nm, CD3CH2F→absorption of a photon→D/F interchange of TS1→CDH2CDF→H/F interchange of TS2→CHD2CHDF→the formation of the major product CHD2+CHDF.

Ab initio CCSD(T)/CBS//ωB97X-D/6-311+G(d,p) calculations of the C6H6N potential energy surface were performed to investigate the reaction mechanism underlying the reaction of atomic nitrogen (2D) with benzene. Thereafter, Rice-Ramsperger-Kassel-Marcus (RRKM) calculations of reaction rate constants and product branching ratios were performed under single-collision conditions. The results revealed that the N(2D) + C6H6 reaction in the case of statistical behavior is expected to produce hydrogen cyanide plus a cyclopentadienyl radical (91.5-88.9%), acetylene plus a pyrrole radical (5.8-7.5%), 1-cyano-2,4-cyclopentadiene + H (2.3-3.0%) and 1-ethynyl-pyrrole + H (0.4-0.6%), with the most favorable pathways being the initial adduct i1 leading to the formation of a seven-membered cyclic intermediate i12 through an exothermic ring expansion process and a multistep route i12 → i15 → i16 → C5H5 + HCN featuring an intramolecular ring-shrinking process involving a C-C bond fusion elimination channel to yield the bicyclic intermediate i15, followed by hydrogen cyanide elimination, thus forming a cyclopentadienyl radical. The calculated product branching ratios were consistent with the available experimental data; however, some quantitative deviations from the experimental results and the possible reasons are also discussed. The possible effects of the title reaction on the upper atmosphere of Titan, with critical implications for the rapid degradation of nitrogen-bearing polycyclic aromatic hydrocarbons, were compared with the mass growth processes of their polycyclic aromatic hydrocarbon counterparts produced through ring expansion.

Soot is formed resulting from incomplete combustion processes of fossil fuels and is one of the most abundant specie in the space. The early stages of soot formation are central to many ongoing studies in combustion research, but its inception and growth are still elusive and highly debated. Herein, molecular dynamic simulations with ab initio based neural network potentials were carried out to simulate the reaction process leading to the growth of PAHs and soot inception from small hydrocarbon reactants. The in silico simulation provided detailed information of reaction paths that revealed critical steps leading to the formation and growth of large PAHs. And the simulation results clearly showed that the formation and growth of possible soot inceptions are achieved through a series of reactions with small PAH radicals, particularly the two-ring PAH radicals rather than by direct combination of large polynuclear hydrocarbons.

Ab initio CCSD(T)/CBS//B3LYP/6-311G(d, p) calculations of the potential energy surface for possible dissociation channels of HOC $_2$ H $_3$ F, as well as Rice-Ramsperger-Kassel-Marcus (RRKM) calculations of rate constants, were carried out, in order to predict statistical product branching ratios in dissociation of HOC $_2$ H $_3$ F at various internal energies. The most favorable reaction pathway leading to the major CH $_2$ CHO+HF products is as the following: OH+C $_2$ H $_3$ F $\rightarrow$ i2 $\rightarrow$ TS14 $\rightarrow$ i6 $\rightarrow$ TS9 $\rightarrow$ i3 $\rightarrow$ TS3 $\rightarrow$ CH $_2$ CHO+HF, where the rate-determining step is HF elimination from the CO bridging position via TS11, lying above the reactants by 3.8 kcal/mol. The CH $_2$ O+CH $_2$ F products can be formed by F atom migration from C $_\beta$ to C $_\alpha$ position via TS14, then H migration from O to C $_\alpha$ position via TS16, and C-C breaking to form the products via TS5, which is 1.8 kcal/mol lower in energy than the reactants, and 4.0 kcal/mol lower than TS11.

NASA's New Horizons mission unveiled a diverse landscape of Pluto's surface with massive regions being neutral in color, while others like Cthulhu Macula range from golden-yellow to reddish comprising up to half of Pluto's carbon budget. Here, we demonstrate in laboratory experiments merged with electronic structure calculations that the photolysis of solid acetylene - the most abundant precipitate on Pluto's surface - by low energy ultraviolet photons efficiently synthesizes benzene and polycyclic aromatic hydrocarbons

The 1-methylvinoxy radical (1-MVO) is an important intermediate in the combustion and tropospheric reaction of OH. However, the vibrational structures of this species and its anionic form, 1-methylvinoxide anion (1-MVO-), are not fully known. Thus, in this study, we obtained the infrared (IR) absorption spectra of 1-MVO and 1-MVO- trapped in a solid Ar matrix. 1-MVO- anions were produced by electron bombardment during matrix deposition of Ar containing a small amount of acetone. The anions were destroyed upon irradiation at 675, 365, and 160 nm, although the formation of 1-MVO was only observed upon irradiation at 675 nm. The assignment of the IR bands of 1-MVO- and 1-MVO was based on the expected chemistry upon photoexcitation and comparison of line wavenumbers, relative IR intensities, and D-isotopic shift ratios with those predicted at the B3LYP/aug-cc-pVTZ level of theory.

This study examined the reaction mechanisms of singlet (rhombic) and triplet (linear) C4 with acetylene by using accurate ab initio CCSD(T)/CBS//B3LYP/6-311G(d,p) calculations followed by a kinetic analysis of various reaction pathways and computations of relative product yields in combustion and planetary atmospheres. These calculations were combined with the Rice–Ramsperger–Kassel–Marcus (RRKM) calculations of reaction rate constants for predicting product-branching ratios, which depend on the collision energy under single-collision conditions. The results demonstrate that the initial reaction begins with the formation of an intermediate 3i2 with an entrance barrier of 3.0 kcal mol−1 and an intermediate 1i1 without entrance barriers. The product-branching ratios obtained by solving kinetic equations with individual rate constants calculated using the RRKM and variational transition-state theories for determining the collision energies between 5 kcal mol−1 and 25 kcal mol−1 demonstrate that l-C6H + H is the dominant reaction product, whereas HC3C3 + H, l-C6 + H2, c-C6H + H, and c-C6 + H2 are minor products. The electronic absorption spectra of solid neon matrices in the range of 17 140–22 200 cm−1 were obtained by Maier et al., and the optimized ground and excited state structures of C6H were used to simulate the absorption spectra by one-photon excitation equations. The displaced harmonic oscillator approximation and the Franck–Condon approximation were used to simulate the absorption spectrum of the B2Π ← X2Π transition of C6H. This indicates that the vibronic structures were dominated by one of the six active completely symmetric modes, with v3 being the most crucial.

We develop a fragment-based ab initio molecular dynamics (FB-AIMD) method for efficient dynamics simulation of the combustion process. In this method, the intermolecular interactions are treated by a fragment-based many-body expansion in which three- or higher body interactions are neglected, while two-body interactions are computed if the distance between the two fragments is smaller than a cutoff value. The accuracy of the method was verified by comparing FB-AIMD calculated energies and atomic forces of several different systems with those obtained by standard full system quantum calculations. The computational cost of the FB-AIMD method scales linearly with the size of the system, and the calculation is easily parallelizable. The method is applied to methane combustion as a benchmark. Detailed reaction network of methane reaction is analyzed, and important reaction species are tracked in real time. The current result of methane simulation is in excellent agreement with known experimental findings and with prior theoretical studies.

Combustion is a kind of important reaction that affects people's daily lives and the development of aerospace. Exploring the reaction mechanism contributes to the understanding of combustion and the more efficient use of fuels. Ab initio quantum mechanical (QM) calculation is precise but limited by its computational time for large-scale systems. In order to carry out reactive molecular dynamics (MD) simulation for combustion accurately and quickly, we develop the MFCC-combustion method in this study, which calculates the interaction between atoms using QM method at the level of MN15/6-31G(d). Each molecule in systems is treated as a fragment, and when the distance between any two atoms in different molecules is greater than 3.5 Å, a new fragment involved two molecules is produced in order to consider the two-body interaction. The deviations of MFCC-combustion from full system calculations are within a few kcal/mol, and the result clearly shows that the calculated energies of the different systems using MFCC-combustion are close to converging after the distance thresholds are larger than 3.5 Å for the two-body QM interactions. The methane combustion was studied with the MFCC-combustion method to explore the combustion mechanism of the methane-oxygen system.

Reactive molecular dynamics (MD) simulation makes it possible to study the reaction mechanism of complex reaction systems at the atomic level. However, the analysis of MD trajectories which contain thousands of species and reaction pathways has become a major obstacle to the application of reactive MD simulation in large-scale systems. Here, we report the development and application of the Reaction Network Generator (ReacNetGenerator) method. It can automatically extract the reaction network from the reaction trajectory without any predefined reaction coordinates and elementary reaction steps. Molecular species can be automatically identified from the cartesian coordinates of atoms and the hidden Markov model is used to filter the trajectory noises which makes the analysis process easier and more accurate. The ReacNetGenerator has been successfully used to analyze the reactive MD trajectories of the combustion of methane and 4-component surrogate fuel for rocket propellant 3 (RP-3), and it has great advantages in terms of efficiency and accuracy compared to traditional manual analysis.

We measured the IR spectra of the solid Ar–trapped chloromethylene (HCCl) prepared by electron bombardment of a CH3Cl/Ar mixture during matrix deposition. Irradiation of matrix samples at 210 nm decreased the intensity of lines corresponding to HCCl, whereas irradiation at 385 nm had an opposite effect. The above behavior allowed an unambiguous identification of all vibrational modes of HCCl, and the obtained assignments were further confirmed by quantum chemical calculations and 13C/2H isotopic labeling experiments.

Two new donor–acceptor conjugated polymers, i.e. PB(C12DTP)V-DTDPP-C12 and PB(C12DTP)V-DTDPP-C12C8, were prepared by the Stille coupling of (E)-1,2-bis(4-dodecyl-6-(trimethylstannyl)-4H-dithieno[3,2-b:2′,3′-d]pyrrol-2-yl)ethene (Sn-B(C12DTP)V) with 3,6-bis(5-bromothiophen-2-yl)-2,5-didodecylpyrrolo[3,4-c]pyrrole-1,4-dione (Br-DTDPP-C12) and 3,6-bis(5-bromo-thiophen-2-yl)-2,5-bis(2-octyldodecyl)pyrrolo[3,4-c]pyrrole-1,4-dione (Br-DTDPP-C8C12), respectively. The molecular weight and thermal properties of the obtained polymers were characterized by gel permeation chromatography (GPC), differential scanning calorimetry (DSC) and thermogravimetry (TG). Their optical and electrochemical properties were analyzed by UV-vis-NIR spectroscopy and cyclic voltammetry (CV). The morphological and molecular-packing features of the polymers were characterized by optical microscopy and atomic force microscopy (AFM), UV polarization spectroscopy and grazing incidence X-ray diffraction (GIXD) to determine the relationship between the structural morphology and the performance. PB(C12DTP)V-DTDPP-C12C8 with branched C12C8 side chains on DPP units shows much higher hole mobility (1.2 cm2 V−1 s−1) than 0.69 cm2 V−1 s−1 of PB(C12DTP)V-DTDPP-C12.

This study examined the reaction mechanisms of singlet (rhombic) and triplet (linear) C4 with acetylene by using accurate ab initio CCSD(T)/CBS//B3LYP/6-311G(d,p) calculations followed by a kinetic analysis of various reaction pathways and computations of relative product yields in combustion and planetary atmospheres. These calculations were combined with the Rice-Ramsperger-Kassel-Marcus (RRKM) calculations of reaction rate constants for predicting product-branching ratios, which depend on the collision energy under single-collision conditions. The results demonstrate that the initial reaction begins with the formation of an intermediate 3i2 with an entrance barrier of 3.0 kcal mol-1 and an intermediate 1i1 without entrance barriers. The product-branching ratios obtained by solving kinetic equations with individual rate constants calculated using the RRKM and variational transition-state theories for determining the collision energies between 5 kcal mol-1 and 25 kcal mol-1 demonstrate that l-C6H + H is the dominant reaction product, whereas HC3C3 + H, l-C6 + H2, c-C6H + H, and c-C6 + H2 are minor products. The electronic absorption spectra of solid neon matrices in the range of 17 140-22 200 cm-1 were obtained by Maier et al., and the optimized ground and excited state structures of C6H were used to simulate the absorption spectra by one-photon excitation equations. The displaced harmonic oscillator approximation and the Franck-Condon approximation were used to simulate the absorption spectrum of the B2Π ← X2Π transition of C6H. This indicates that the vibronic structures were dominated by one of the six active completely symmetric modes, with v3 being the most crucial.

The reactive molecular dynamics is widely used in the field of computational chemistry to study the reaction mechanisms in molecular systems. However, complex trajectories that are difficult to analyze have become a major obstacle to its application in large-scale systems. In this work, a new approach named ReacNetGen is developed to obtain reaction networks based on reactive MD simulations. Molecular species can be automatically generated from the 3D coordinates of atoms in the trajectory. The hidden Markov model is used to filter the noises in the trajectory, which makes the analysis process easier and more accurate. Compared with manual analysis, the advantage of this method in terms of efficiency is very obvious for large-scale simulation trajectories. It has been successfully used in the analysis of the simulated oxidation of 4-component RP-3 and methane.

This study examined the formation mechanisms of singlet (rhombic) and triplet (linear) C4 with acetylene by using accurate ab initio CCSD(T)/cc-pVTZ/B3LYP/6-311G(d,p) calculations, followed by a kinetic analysis of various reaction pathways and computations of relative product yields in combustion and planetary atmospheres. These calculations were combined with the Rice–Ramsperger–Kassel–Marcus (RRKM) calculations of reaction rate constants for predicting product-branching ratios, which depend on the collision energy under single-collision conditions. The results show that the initial reaction begins with the formation of an intermediate t-i2, with entrance barriers of 3.8 kcal/mol, and an intermediate s-i1 without entrance barriers. On the triplet surface, the t-i2 rearranged the other C6H2 isomers, including t-i3, t-i4, and t-i6, through hydrogen migration; the t-i2, t-i3, t-i4, t-i5, and t-i6 isomers lost a hydrogen atom, and produced the most stable linear isomer of C6H, with an overall reaction exothermicity of 11 kcal/mol. Hydrogen elimination from the t-i10 isomer led to the formation of the annular C6H isomer, HC3C3 + H, at 23.9 kcal/mol above l-C4 + C2H2. On the singlet surfaces, s-i1 rearranged the other C6H2 isomers, including s-i2 and s-i4, through carbon–carbon bond cleavage. The s-i6 and s-i11 isomers also lost a hydrogen atom, and produced the linear C6H radical. Hydrogen elimination from the s-i4 isomer led to the formation of the annular C6H isomer. The s-i5 lost a hydrogen atom, and produced the six-member ring c-C6H isomer, at 2.1 kcal/mol higher than l-C4 + C2H2. The 1,1-H2 loss from the s-i10 isomer produced the linear hexacarbon l-C6 + H2 product, with an endothermicity of 2.3 kcal/mol and a 1,1-H2 loss from the s-i11 isomer, producing in the cyclic hexacarbon c-C6 + H2 product, with an exothermicity of 11.2 kcal/mol. The product-branching ratios obtained by solving kinetic equations with individual rate constants calculated using the RRKM and VTST theories for determining the collision energies between 5 kcal/mol and 25 kcal/mol show that l-C6H + H is the dominant reaction product, whereas HC3C3 + H, l-C6 + H2, c-C6H + H, and c-C6 + H2 are minor products with branching ratios. The s-i6 isomer was calculated to be the most stable C6H2 species, even more favorable than t-i3 (by 76 kcal/mol).

The reactive molecular dynamics is widely used in the field of computational chemistry to study the reaction mechanisms in molecular systems. However, complex trajectories that are difficult to analyze have become a major obstacle to its application in large-scale systems. In this work, a new approach named ReacNetGen is developed to obtain reaction networks based on reactive MD simulations. Molecular species can be automatically generated from the 3D coordinates of atoms in the trajectory. The hidden Markov model is used to filter the noises in the trajectory, which makes the analysis process easier and more accurate. Compared with manual analysis, the advantage of this method in terms of efficiency is very obvious for large-scale simulation trajectories. It has been successfully used in the analysis of the simulated oxidation of 4-component RP-3 and methane.

The equilibrium geometry and 75 vibrational normal-mode frequencies of the ground and first excited states of protonated pyrene isomers were calculated and characterized in the adiabatic representation by using the complete active space self-consistent field (CASSCF) method. Electronic absorption spectra of solid neon matrixes in the wavelength range 495-415 nm were determined by Maier et al. and they were analyzed using time-dependent density functional theory calculations (TDDFT). CASSCF calculations and absorption and emission spectra simulations by one-photon excitation equations were used to optimize the excited and ground state structures of protonated pyrene isomers. The absorption band was attributed to the S0 → S1 electronic transition in 1H-Py(+), and a band origin was used at 20580.96 cm(-1). The displaced harmonic oscillator approximation and Franck-Condon approximation were used to simulate the absorption spectrum of the (1) (1)A' ← X[combining tilde](1)A' transition of 1H-Py(+), and the main vibronic transitions were assigned for the first ππ* state. It shows that the vibronic structures were dominated by one of the eight active totally symmetric modes, with ν15 being the most crucial. This indicates that the electronic transition of the S1((1)A') state calculated in the adiabatic representation effectively includes a contribution from the adiabatic vibronic coupling through Franck-Condon factors perturbed by harmonic oscillators. The present method can adequately reproduce experimental absorption and fluorescence spectra of a gas phase.

Regarding CH3OH+ and CH3OH++, theoretical calculations have used a variety of methods to describe geometric structures and potential energy surfaces. Rice–Ramsperger–Kassel–Marcus (RRKM) theory has been applied to compute the rate constants and product branching ratios of various channels on potential energy surfaces. The dissociate ions produced from CH3OH+ include CH2+, HCOH+ and CH2OH+, whereas H+, H2+, H3+, COH+/HCO+, and CH3O+ fragments are generated from CH3OH++. By roaming, we imply that a neutral hydrogen molecule fragment explores relatively flat regions of the intrinsic reaction coordinate calculations from the minimum energy path.

The direct infrared (IR) absorption spectra of propargyl cations were recorded. These cations were generated via the electron bombardment of a propyne/Ar matrix sample during matrix deposition. Secondary photolysis with selected ultraviolet (UV) light was used for grouping the observed bands of various products. The band assignment of the propargyl cation in solid Ar was performed according by referring to the previous infrared photodissociation (IRPD) and velocity-map imaging photoelectron (VMI-PE) data, and via theoretical predictions of the anharmonic vibrational wavenumbers, band intensities, and deuterium-substituted isotopic ratios. Almost all the IR active bands with an observable intensity were recorded and the ν11 mode was reported for the first time.

Electron bombardment during deposition of an Ar matrix containing a small proportion of allene generated allene cations. Further irradiation of the matrix sample at 385 nm destroyed the allene cations and formed propyne cations in solid Ar. Both cations were identified according to previously reported IR absorption bands. Using a similar technique, we recorded the ultraviolet absorption spectrum of allene cations in solid Ar. The vibrationally resolved progression recorded in the range of 266–237 nm with intervals of about 800 cm−1 was assigned to the A 2E ← X 2E transition of allene cations, and the broad continuum absorption recorded in the region of 229–214 nm was assigned to their B 2A1 ← X 2E transition. These assignments were made based on the observed photolytic behavior of the progressions and the vertical excitation energies and oscillator strengths calculated using time-dependent density functional theory.

Allene and propyne as well as their cationic forms play important roles in combustion and interstellar chemistry and serve as a model system for molecular spectroscopic studies. Both cations show Jahn–Teller (J–T) distortions in their ground states. These J–T distortions make the theoretical and experimental studies of their electronic structures difficult. We produced allene cations upon electron bombardment during matrix deposition of Ar containing a small proportion of allene. The intensities of the absorption features of the allene cation decreased after irradiation with UV light, whereas new bands attributed to propyne cations increased. The observed line wavenumbers, relative intensities, and deuterium-substituted isotopic ratios of the isomers of C3H4+ agree satisfactorily with those predicted by density functional theory at the B3PW91/aug-cc-pVTZ level of theory. This method produced the hydrocarbon cations of interest with few other fragments that enabled the clear identification of the IR spectr...

We recorded the IR spectra of C 2 H 4 + trapped in solid Ar through electron bombardment of a mixture of ethylene and Ar during matrix deposition. The four most intense lines of C 2 H 4 + were observed and assigned according to comparison with the literature data for ethylene with solid Ne and the predicted vibrational anharmonic wavenumbers. Experiments involving further UV irradiations of the matrix samples were performed in the region 345–225 nm. Upon UV radiation, lines of C 2 H 4 + decreased and lines corresponding to C 2 H 4 , C 2 H 2 , and C 2 H 3 increased, indicating that the photodissociation and photo-assisted neutralization of C 2 H 4 + in the matrix may occur simultaneously.

To facilitate direct spectroscopic observation of hydrogen chloride anions (HCl−), electron bombardment of CH3Cl diluted in excess Ar during matrix deposition was used to generate this anion. Subsequent characterization were performed by IR spectroscopy and quantum chemical calculations. Moreover the band intensity of HCl− decays slowly when the matrix sample is maintained in the dark for a prolonged time. High-level ab inito calculation suggested that HCl− is only weakly bound. Atom-in-molecule charge analysis indicated that both atoms of HCl− are negatively charged and the Cl atom is hypervalent.

Repetitive DNA sequences are ubiquitous in life, and changes in the number of repeats often have various physiological and pathological implications. DNA repeats are capable of interchanging between different noncanonical and canonical conformations in a dynamic fashion, causing configurational slippage that often leads to repeat expansion associated with neurological diseases. In this report, we used single-molecule spectroscopy together with biophysical analyses to demonstrate the parity-dependent hairpin structural polymorphism of TGGAA repeat DNA. We found that the DNA adopted two configurations depending on the repeat number parity (even or odd). Transitions between these two configurations were also observed for longer repeats. In addition, the ability to modulate this transition was found to be enhanced by divalent ions. Based on the atomic structure, we propose a local seeding model where the kinked GGA motifs in the stem region of TGGAA repeat DNA act as hot spots to facilitate the transition between the two configurations, which may give rise to disease-associated repeat expansion.

Hypervalent molecules are one of the exceptions to the octet rule. Bonding in most hypervalent molecules is well rationalized by the Rundle–Pimentel model (three-center four-electron bond), and high ionic bonding between the ligands and the central atom is essential for stabilizing hypervalent molecules. Here, we produced one of the simplest hypervalent anions, HF−, which is known to deviate from the Rundle–Pimentel model, and identified its ro-vibrational features. High-level ab inito calculations reveal that its bond dissociation energy is comparable to that of dihalides, as supported by secondary photolysis experiments with irradiation at various wavelengths. The charge distribution analysis suggested that the F atom of HF− is negative and hypervalent and the bonding is more covalent than ionic.

We observed the products C 4 H 5 , C 4 H 4 , C 3 H 3 and CH 3 of the C( 3 P) + C 3 H 6 reaction using product time-of-flight spectroscopy and selective photoionization. The identified species arise from the product channels C 4 H 5 + H, C 4 H 4 + 2H and C 3 H 3 + CH 3 . Product isomers were identified via measurements of photoionization spectra and calculations of adiabatic ionization energy. Product C 4 H 5 probably involves three isomers HCCCHCH 3 , H 2 CCCCH 3 and H 2 CCCHCH 2 . In contrast, products C 4 H 4 and C 3 H 3 involve exclusively HCCCHCH 2 and H 2 CCCH, respectively. Reaction mechanisms are unraveled with crossed-beam experiments and quantum-chemical calculations. The 3 P carbon atom attacks the π orbital of propene (C 3 H 6 ) to form a cyclic complex c -H 2 C(C)CHCH 3 that rapidly opens the ring to form H 2 CCCHCH 3 followed by decomposition to HCCCHCH 3 /H 2 CCCCH 3 /H 2 CCCHCH 2 + H and H 2 CCCH + CH 3 ; the corresponding branching ratios are 7:5:10:78 predicted with RRKM calculations at collision energy 4 kcal mol −1 . Nascent C 4 H 5 with enough internal energy further decomposes to HCCCHCH 2 + H. Ratios of products C 4 H 5 , C 4 H 4 and C 3 H 3 are experimentally evaluated to be 17:8:75. This work provides a comprehensive look at product channels of the title reaction and gives implications for the formation of hydrocarbons in extra-terrestrial environments such as Titan and carbon-rich interstellar media. We suggest that the title reaction, hitherto excluded in any chemical networks, needs to be taken into account at least in the atmosphere of Titan and carbon-rich molecular clouds where rapid neutral–neutral reactions are dominant and carbon atoms and propene are abundant.

We investigated the title reaction at collision energy 3.5 kcal mol(-1) in a crossed molecular beam apparatus using undulator radiation as an ionization source. Time-of-flight (TOF) spectra of product C(3)H(3) were measured in laboratory angles from 20° to 100° using two photoionization energies 9.5 and 11.6 eV. These two sets of experimental data exhibit almost the same TOF distributions and laboratory angular distributions. From the best simulation, seven angle-specific kinetic-energy distributions and a nearly isotropic angular distribution are derived for product channel C(3)H(3) + H that has an average kinetic-energy release of 15.5 kcal mol(-1), corresponding to an average internal energy of 33.3 kcal mol(-1) in C(3)H(3). Furthermore, TOF spectra of product C(3)H(3) were measured at laboratory angle 52° with ionizing photon energies from 7 to 12 eV. The appearance of TOF spectra remains almost the same, indicating that a species exclusively contributes to product C(3)H(3); the species is identified as H(2)CCCH (propargyl) based on the ionization energy of 8.6 ± 0.2 eV and the maximal kinetic-energy release of 49 kcal mol(-1). Theoretical calculations indicate that the rapid inversion mechanism and rotation in intermediate H(2)CCCH(2) can result in a forward-backward symmetric angular distribution for product C(3)H(3) + H. The present work avoids the interference of reactions of C((1)D) and C(2) radicals with C(2)H(4) and rules out the probability of production of other isomers like c-C(3)H(3) and H(3)CCC proposed in the previous work at least at the investigated collision energy.

The infrared (IR) spectrum of borane(3) anions (BH3−) isolated in solid Ar was recorded; two vibrational modes were observed at 2259.4 and 606.6 cm−1, which were assigned to the BH2 stretching (ν3) and out-of-plane large-amplitude (ν2) modes, respectively. These anions were produced by the electron bombardment of an Ar matrix sample containing a small proportion of B2H6 and H2 during matrix deposition or by the photolysis of single-bridged-B2H5− in an Ar matrix with the selected ultraviolet light. The band positions, relative intensity ratios, isotopic splitting pattern, and isotopic shift ratios of the observed IR features of BH3− are generally in good agreement with those predicted by the B2PLYP/aug-cc-pVTZ method.

The mechanisms of ionization and dissociation of cyclohexanone (C6H10O) in a 90 fs, 788 nm linearly polarized laser field ranging from 1013 to 1014 W/cm2 by a time-of-flight mass spectrometer (TOF-MS) have been investigated. The ion yields as a function of laser intensity have been measured experimentally. By comparison with the Ammosov-Delone-Krainov (ADK) theory based on a hydrogen-like model, the ionization mechanism of cyclohexanone in this intense femtosecond laser field has been understood. Considering the importance of molecular nuclear motions, we propose that the Franck-Condon (F-C) factor can provide the excess vibrational energy in the molecular ion. This energy is required for the decomposition of the molecular ion which finally results in the observed mass spectrum.

The equilibrium geometry and 24 vibrational-normal-mode frequencies of the excited state S2(1B2u) of pyrazine are calculated and characterized using the complete active space self-consistent field method in the adiabatic representation. The displaced harmonic oscillator approximation is used to simulate the absorption spectrum of the S2(1B2u) state along with the Franck–Condon approximation. It is found that the totally symmetric mode ν1 plays the most important role and this exactly agrees with the experimental observations. The simulated absorption spectrum agrees well with those experimentally observed. This indicates that the present S2(1B2u) state calculated in the adiabatic representation effectively includes contribution from the diabatic vibronic coupling through the conical intersection.

Making use of a set of quantum chemistry methods, the harmonic potential surfaces of the ground state (S0(1Ag)) and the first (S1(1B3u)) excited state of pyrazine are investigated, and the electronic structures of the two states are characterized. In the present study, the conventional quantum mechanical method, taking account of the Born-Oppenheimer adiabatic approximation, is adopted to simulate the absorption spectrum of S1(1B3u) state of pyrazine. The assignment of main vibronic transitions is made for S1(1B3u) state. It is found that the spectral profile is mainly described by the Franck-Condon progression of totally symmetric mode ν6a. For the five totally symmetric modes, the present calculations show that the frequency differences between the ground and the S1(1B3u) state are small. Therefore the displaced harmonic oscillator approximation along with Franck-Condon transition is used to simulate S1(1B3u) absorption spectra. The distortion effect due to the so-called quadratic coupling is demonstrated to be unimportant for the absorption spectrum, except the coupling mode ν10a. The calculated S1(1B3u) absorption spectrum is in reasonable agreement with the experimental spectra.

A set of harmonic potential surfaces have been obtained at the CASSCF/6-311+G** level for the ground, n–p*, and p–p* states of 9Hadenine. They have been used to analyze experimental R2PI and resonance fluorescence spectra and the excited state lifetimes of adenine. A tentative plausible assignment has been proposed, which takes into account a strong coupling between these electronic states. Using the potential surfaces, the excess energy dependence of the excited state lifetimes of adenine has been interpreted, and the lifetime of the n–p * state at the band origin has also been estimated to be in the order of 10 ns.

Two series of single phase triple-perovskite superconducting samples with nominal compositions of (Nd 1− x Ca x )Ba 2 Cu 3 O y and Nd(Ba 2− x Ca x )Cu 3 O y are prepared by the solid-state reaction method. It is found that both the T c and the orthorhombicity of the unit cell for all the samples decrease with increasing Ca content. T c is also correlated to the distance of Cu(2)–Cu(2) along the c -axis, which decreases linearly with increasing Ca doping.

Potential energy surfaces of various reactions in the BO/H 2 , B 2 O 2 /H 2 , and BS/H 2 systems have been studied at the G2M(MP2)//B3LYP/6-311+G(d,p) level of theory. The BO + H 2 reaction is shown to proceed by ion of a hydrogen atom by B to produce OBH + H with the barrier and exothermicity of 8.3 and 6.8 kcal/mol, respectively. The reaction can also occur by 1,2-insertion of BO into the H-H bond or by H ion by the O atom; however, the barriers for these channels are much higher, 36.4 and 42.7 kcal/mol, respectively. Via a low ∼0.3 kcal/mol barrier, the OBH + H reaction produces the OBH 2 radical, which is the most stable compound in the BO/H 2 system and lies 15.9, 2.5, and 4.2 kcal/mol below BO + H 2 , trans-HBOH, and cis-HBOH, respectively. OBH 2 can isomerize to trans-HBOH overcoming a barrier of 27.7 kcal/ mol and the latter can rearrange to the cis conformer with a barrier of 10.8 kcal/mol. BOH and H can recombine and form cis- or trans-HBOH without barriers. In the B + H 2 O reaction, the reactants can first form a weakly bound B-H 2 O complex, which then can eliminate an H atom producing BOH + H or undergo insertion of B into an O-H bond giving trans-HBOH with barriers of 4.7 and 6.2 kcal/mol relative to the initial reactants, respectively, and trans-HBOH can eventually decompose to OBH + H and a minor amount of BO + H 2 . Singlet OBBO is shown to be much less reactive with respect to H 2 than the BO monomer. Alternatively, after two BO recombine to form a triplet OBBO molecule over a moderate 8.3 kcal/mol barrier, t-OBBO can easily react with H 2 producing either BO + OBH 2 (via a t-OBBH 2 O intermediate) or OBBOH + H with barriers of 4.4 and 7.4 kcal/mol, respectively. The reactions in the BS/H 2 system are shown to be similar to those for BO/H 2 , except that BS cannot insert into H 2 , SBH 2 resides in a much deeper potential well (37.3 kcal/mol below BS + H 2 ) and can rearrange both to trans- and cis-HBSH, the B-H 2 S complex is more strongly bound than B-H 2 O, and the B + H 2 S reaction is expected to be significantly faster than the reaction of B + H 2 O.

The reaction C2 + C6H2 → C8H + H was investigated for the first time. Reactant C2 (C6H2) was synthesized from 1% C3F6/He (5% C2H2/He) by pulsed high-voltage discharge. We measured the translational-energy distribution, the angular distribution, and the photoionization spectrum of product C8H in a crossed molecular-beam apparatus using synchrotron vacuum-ultraviolet ionization. This reaction released average translational energy of 8.5 kcal mol(-1) corresponding to a fraction of 0.37 in translation. C8H was identified as octatetranyl based on the maximal translational-energy release 23 ± 2 kcal mol(-1) and the ionization threshold 8.9 ± 0.2 eV. Kinematic constraints can qualitatively account for the nearly isotropic angular distribution. The quantum-chemical calculations indicate that the exothermic reactions C2 (X (1)Σg (+)/a (3)Πu) + HC6H → C8H + H can proceed without entrance and exit barriers, implying the importance in the cold interstellar medium. This work verifies that interstellar C8H can be formed through the C2 + C6H2 reaction.

The reaction C3(a(3)Πu) + C2H2 → C5H + H was investigated at collision energy 10.9 kcal mol(-1) that is less than the enthalpy of ground-state reaction C3(X(1)Σg (+)) + C2H2 → C5H + H. C3(a(3)Πu) radicals were synthesized from 1% C4F6/He by pulsed high-voltage discharge. The title reaction was conducted in a crossed molecular-beam apparatus equipped with a quadrupole-mass filter. Product C5H was interrogated with time-of-flight spectroscopy and synchrotron vacuum-ultraviolet ionization. Reactant C3(a(3)Πu) and product C5H were identified using photoionization spectroscopy. The ionization thresholds of C3(X(1)Σg(+)) and C3(a(3)Πu) are determined as 11.6 ± 0.2 eV and 10.0 ± 0.2 eV, respectively. The C5H product is identified as linear pentynylidyne that has an ionization energy 8.4 ± 0.2 eV. The title reaction releases translational energy 10.6 kcal mol(-1) in average and has an isotropic product angular distribution. The quantum-chemical calculation indicates that the C3(a(3)Πu) radical attacks one of the carbon atoms of C2H2 and subsequently a hydrogen atom is ejected to form C5H + H, in good agreement with the experimental observation. As far as we are aware, the C3(a(3)Πu) + C2H2 reaction is investigated for the first time. This work gives an implication for the formation of C5H from the C3(a(3)Πu) + C2H2 reaction occurring in a combustion or discharge process of C2H2.

We investigated the dynamics of the reaction of (3)P atomic carbon with propene (C3H6) at reactant collision energy 3.8 kcal mol(-1) in a crossed molecular-beam apparatus using synchrotron vacuum-ultraviolet ionization. Products C4H5, C4H4, C3H3, and CH3 were observed and attributed to exit channels C4H5 + H, C4H4 + 2H, and C3H3 + CH3; their translational-energy distributions and angular distributions were derived from the measurements of product time-of-flight spectra. Following the addition of a (3)P carbon atom to the C=C bond of propene, cyclic complex c-H2C(C)CHCH3 undergoes two separate stereoisomerization mechanisms to form intermediates E- and Z-H2CCCHCH3. Both the isomers of H2CCCHCH3 in turns decompose to C4H5 + H and C3H3 + CH3. A portion of C4H5 that has enough internal energy further decomposes to C4H4 + H. The three exit channels C4H5 + H, C4H4 + 2H, and C3H3 + CH3 have average translational energy releases 13.5, 3.2, and 15.2 kcal mol(-1), respectively, corresponding to fractions 0.26, 0.41, and 0.26 of available energy deposited to the translational degrees of freedom. The H-loss and 2H-loss channels have nearly isotropic angular distributions with a slight preference at the forward direction particularly for the 2H-loss channel. In contrast, the CH3-loss channel has a forward and backward peaked angular distribution with an enhancement at the forward direction. Comparisons with reactions of (3)P carbon atoms with ethene, vinyl fluoride, and vinyl chloride are stated.