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We perform accurate quantum dynamics calculations on the isomerization of vinylidene-acetylene. Large-scale parallel computations are accomplished by an efficient theoretical scheme developed by our group, in which the basis functions are customized for the double-H transfer process. The A′1 and B″1 vinylidene and delocalization states are obtained. The peaks recently observed in the cryo-SEVI spectra are analyzed, and very good agreement for the energy levels is achieved between theory and experiment. The discrepancies of energy levels between our calculations and recent experimental cryo-SEVI spectra are of similar magnitudes to the experimental error bars, or ≤30 cm−1 excluding those involving the excitation of the CCH2 scissor mode. A kind of special state, called the isomerization state, is revealed and reported, which is characterized by large probability densities in both vinylidene and acetylene regions. In addition, several states dominated by vinylidene character are reported for the first time. The present work would contribute to the understanding of the double-H transfer.

The present calculations reveal the effects of intersystem crossings and spin–orbit couplings on laser cooling of the group VA hydrides, with an empirical law of “crossing point shifting down” down a group in the periodic table generalized.

We present an in-depth theoretical study of the C(1D) + HD (v = 0, j = 0) → CD (CH) (v', j') + H (D) reaction using a time-dependent wave packet method with full Coriolis coupling on the Zhang-Ma-Bian potential energy surfaces (PESs) recently constructed by our group. The integral cross sections (ICS), differential cross sections, CD/CH branching ratios, and product state distributions are calculated over a wide range of collision energies. We find that the vibrational branching ratio defined as ICS(v'=1)/ICS(v'=0) obtained from the b1A″ PES is much smaller than that from the a1A' PES for both product channels, which may be attributed to the dynamical effects of the conical intersection regulated (CI-R) intermediate on the b1A″ PES. The collision energy dependence of CD/CH branching ratios displays oscillatory structures, which may be caused by the resonance states supported by the wells on the PESs. The high-temperature rate coefficients are also obtained and compared with previous results. The role of the excited-state PESs is also discussed.

Laser cooling of polyatomic molecules to the ultracold regime may enable some new science and technology applications; however, the related study is still at its very early stage. Here, by means of accurate ab initio and dynamical calculations, we identify two new candidate tetratomic molecules that are suitable for laser cooling and demonstrate the feasibility and advantage of two laser cooling schemes that are able to produce ultracold CaCCH and SrCCH molecules. The internally contracted multiconfiguration reference configuration interaction method is applied, and excellent agreement is achieved between the computed and experimental spectroscopic data. We find that the X2Σ1/2+→A2Π1/2 transitions for both candidates feature diagonal Franck–Condon factors, short radiative lifetimes, and no interference from intermediate electronic states. In addition, the crossings with higher electronic states do not interfere. We further construct feasible laser cooling schemes for CaCCH and SrCCH, each of which allows scattering 104 photons for direct laser cooling. The estimated Doppler temperatures for both CaCCH and SrCCH are on the order of μK.

Recognition of molecular structural features is one of the most attractive fields in chemistry, especially when combining with machine learning techniques. Pattern recognition techniques are straightforward in recognizing graphic features, but little attention was given to recognize molecular structural features. In this work, we propose a new method taking advantage of pattern recognition techniques to analyze structural features and obtain novel chemical insights. Specifically, the cluster analysis is presented to recognize structural features, which provides an alternative to the most widely used root mean square deviation (RMSD) method and the recently proposed blob detection method. Based on this, the convex hull of the molecule is constructed. The convex hull of molecules is highly appealing in the sense that one can introduce established theorems and properties from other disciplines into chemistry. Novel molecular descriptors based on convex hulls can be defined and show encouraging results, especially in providing new insights in understanding non-covalent interactions, adsorption processes, etc.

The van der Waals (vdW) interaction is very important in fields of physics, biology and chemistry, and its role in reaction dynamics is an issue of great interest. In this review, we focus on the recent progresses in the theoretical and experimental studies on the vdW interaction in bimolecular reactions. In particular, we review those studies that have advanced our understanding of how the vdW interaction can strongly influence the dynamics in both direct activated and complex-forming reactions, and further extend the discussion to the polyatomic reactions involving more atoms and those occurring at cold and ultracold temperatures. We indicate that an accurate description of the delicate vdW structure and long-range potential remains a challenge nowadays in either ab initio calculations or the fitting of the potential energy surfaces. We also present an explanation on the concept of vdW saddle proposed by us recently which may have general importance.

Poly(carborane-siloxane) polymers were successfully synthesized by tris(pentafluorophenyl)borane catalyzing diorganohydroxysilanes (Si OH) and dihydrosilanes (Si H) to form siloxane bond and release hydrogen. The structure of monomers and polymers were characterized by 1H, 13C, 29Si NMR and FI-IR. Furthermore, in the present study, the qualitative characterization of silicon hydrogen bond in dihydrosilanes activated by catalyst B(C6F5)3 was investigated by 1H NMR relaxation test and theoretical calculation. The results shown that silicon hydrogen bond (Si H) and B(C6F5)3 form the complex [Si⋯H⋯B(C6F5)3] which is relevant to chemical reactivity. In addition, dihydrosilanes exhibit the following reactive activity order: 1,1,3,3-tetramethyldisiloxane > 1,7-bis(3-hydridotetramethyldisiloxanyl)-m-carborane > diphenylsilane > methylphenylsilane > 1,7-bis(dimethylsilyl)-m-carborane. This synthetic method offers a new effective approach to synthesize poly(carborane-siloxane) polymers and the reactive activity order has a guide significance for experimental system design.

Recent studies on the exothermic complex-forming reactions have improved our understanding of complex-forming reactions greatly, however, so far a similar level of study on endothermic ones has been rather limited. In this work, the endothermic complex-forming reaction Si(1D) + H2 → SiH + H and its deuterated isotopic variant are investigated by quantum dynamics (QD) and ring polymer molecular dynamics (RPMD) calculations on a new global ab initio potential energy surface (PES) for the ground electronic state, which is constructed based on 8996 symmetry unique points computed at the icMRCI+Q/aug-cc-pVQZ level. The PES reproduces our ab initio data very well in the dynamically important regions, on which the ro-vibrational energy levels of SiH2 are calculated and general good agreement with experiment is obtained. The integral cross sections and product angular and state distributions are computed in a wide range of collision energies, and interesting dynamics behaviors are revealed. The rate coefficients are also investigated, which display an exponential rise from 2.09 × 10-20 to 6.00 × 10-12 cm3 s-1 for the Si(1D) + H2 reaction as the temperature increases from 300 to 1500 K, in contrast to the nearly temperature-independent behavior of exothermic complex-forming reactions. In addition, the applicability of the RPMD approach is demonstrated, and the kinetic isotope effect is investigated, the ratio of which decreases from 7.89 (300 K) to 1.70 (1500 K). The effects of tunneling and initial rotational excitation are also discussed.

We present accurate quantum dynamics calculations on vinylidene-d2 (fully deuterated vinylidene) isomerization. This is achieved by large-scale parallel computations with an efficient theoretical scheme developed by us in which basis functions are customized for the deuterium migration process. Mode-specific permutation tunneling splittings of vinylidene-d2 states are reported here for the first time, and evident isotope effects are revealed. The A1 ', B2 ', A1 ″, and B2 ″ symmetric vinylidene-d2 states are calculated, and the peaks recently observed in the cryo-SEVI spectra are analyzed, with very good agreement between theory and experiment achieved for the energy levels. In addition, a few vinylidene-d2 states beyond the experimental energy region are reported. Our studies are helpful for acquiring a better understanding of isotope effects in the double-hydrogen migration processes.

The formic acid dimer (FAD) is an important benchmark system for understanding the double hydrogen transfer process. Most recently, Zhang et al. measured a few tunneling splittings upon fundamental excitation of FAD precisely (Zhang, Y. et al. J. Chem. Phys. 2017, 146, 244306); however, relevant theoretical studies are very limited. Here, we present a multidimensional quantum dynamics study on mode-specific tunneling splittings upon fundamental excitation in FAD with an efficient theoretical scheme developed by our group in which the process-oriented basis function customization strategy is combined with the preconditioned inexact spectral transform method. Various mode-specific tunneling splittings upon fundamental excitation are systematically calculated, and interesting mode-specific excitation effects on tunneling rate are identified. In particular, the calculated tunneling splittings for the ν22 and ν21 states are in good agreement with experiment, and the remarkable mode-specific suppression effects upon excitation should result from that the antisymmetric vibrational modes hinder the concerted double H-transfer. The present work is helpful to acquire a better understanding of the mode-specific excitation effects on tunneling processes.

The application of low-fragmentation mass spectrometry to identify chemicals has been recognized to be of particular importance in chemistry, biomedicine, and materials science. Utilizing a customized all-solid-state picosecond-pulsed deep-ultraviolet (DUV) laser, here we present new advances into photoionization mass spectrometry. The DUV laser ionization mass spectrometry (DUV-LIMS) results in very clean spectra pertaining to minimized structure relaxation and fragmentation under the ultrafast ionization process. Typical DUV-LIMS applications are illustrated not only for small organic molecules but also for long-chain unsaturated hydrocarbons and clusters of benzene. The unique advantages of DUV-LIMS enable us to detect and analyze confusing organic compound mixtures, indicating promising applications. DUV-LIMS is also found to be applicable in the identification of phenylenediamine isomers. An in-depth analysis of reaction dynamics is provided showing how hydrogen-atom-transfer (HAT) initiates the distinguishable photodissociation of phenylenediamines under near-resonant excitation. In particular, ortho-phenylenediamine (OPD) finds a remarkable dehydrogenation product with comparable intensity to the molecular ion peak, which is associated with the quantum tunnelling tautomers, providing new subjects for studying intramolecular noncovalent interactions.

The feasibility of direct laser cooling of silicon monofluoride (SiF) is investigated and assessed using the internally contracted multireference configuration interaction method with the Davidson correction and entirely uncontracted aug-cc-pwCV5Z basis sets. As for the A 2 Σ + ( ν ′ = 0 ) → X 2 Π transition, the computed radiative lifetime is 0.69 μs and the vibrational branching ratio R ν ′ ν is highly diagonally distributed with the R 00 being 0.994, which are desirable for rapid and efficient laser cooling. In addition, good agreement is achieved between our computed spectroscopic properties and the available experimental data for the X 2 Π and A 2 Σ + states of SiF. We propose a kind of laser cooling scheme, in which the wavelengths are located in the visible region. Both our calculated Doppler and recoil temperatures are of the order of μ K, and the calculated minimum distance necessary to bring the velocity of a SiF beam to that suitable for trapping is 13 cm, indicating that the SiF molecule can be cooled to the ultracold regime through the proposed scheme.

The isotopic product CD/CH branching ratios, thermal rate coefficients, as well as other dynamical quantities of the C(1D) + HD → CD(H) + H(D) reaction are investigated by detailed quasiclassical trajectory calculations on the highly accurate singlet ground-state (a1A′) and the first excited-state (1A′′) global ab initio potential energy surfaces (PESs) recently constructed by us. The calculated CD/CH branching ratios are in reasonable agreement with experiment. The thermal rate coefficients in the temperature range of 200–1500 K are calculated, and the obtained values at room temperature are in very good agreement with available experimental data. The distinct topographical features between the present and previous PESs, which influence the CD/CH branching ratio, are also discussed. In addition, the effect of the 1A′′ PES is investigated, and the results show that the contribution from the 1A′′ PES to the total reactivity is rather noticeable.

The importance of conical intersections (CIs) in electronically nonadiabatic processes is well known, but their influence on adiabatic dynamics has been underestimated. Here, through combined experimental and theoretical studies, we show that CIs induce a barrier and regulate conversion from a precursor metastable intermediate (CI-R) to a deep well one. This results in bond-selective activation, influencing the adiabatic dynamics markedly in the C(1D) + HD reaction. Theory is validated by experiment; quantum dynamics calculations on highly accurate ab initio potential energy surfaces yield rate coefficients and product branching ratios in excellent agreement with the experiment. Quasi-classical trajectory calculations reveal that the CI-R intermediate leads to unusual reaction mechanisms (designated as C─H activation complex conversion and cyclic complex), which are responsible for large branching ratios. We also reveal that CI-R intermediates exist in other reactive systems, and the dynamical effects uncovered here may have general significance.

The reaction of C3H8+O(3P)→C3H7+OH is investigated using ab initio calculation and dynamical methods. Electronic structure calculations for all stationary points are obtained using a dual-level strategy. The geometry optimization is performed using the unrestricted second-order Moller-Plesset perturbation method and the single-point energy is computed using the coupled-cluster singles and doubles augmented by a perturbative treatment of triple excitations method. Results indicate that the main reaction channel is C3H8+O(3P)→i-C3H7+OH. Based upon the ab initio data, thermal rate constants are calculated using the variational transition state theory method with the temperature ranging from 298 K to 1000 K. These calculated rate constants are in better agreement with experiments than those reported in previous theoretical studies, and the branching ratios of the reaction are also calculated in the present work. Furthermore, the isotope effects of the title reaction are calculated and discussed. The present w...

The feasibility of direct laser cooling of copper monofluoride (CuF) is investigated and assessed using ab initio methods with the inclusion of spin–orbit coupling (SOC) effects. Seven low-lying Λ–S states are calculated using an explicitly correlated multireference configuration interaction method with the Davidson correction (MRCI-F12 + Q). The spectroscopic properties of the Ω states are calculated, which are in very good agreement with the available experimental measurements and indicate that the influence of SOC effects is evident. We find that, the radiative lifetimes of transitions A(ν′ = 0) → a3Σ+1, b3Π1,0+ are much longer than that of the A(ν′ = 0) → X(ν = 0) transition; the vibrational branching ratios Rν′ν for the A(ν′) ← X(ν) transition are highly diagonally distributed with R00 being 0.991; and the evaluated transition wavelengths are located in the visible region. We further propose a laser cooling scheme based on the A(ν′) ← X(ν) transition, with which the laser cooling of CuF can be realized effectively. Moreover, a photoionization method is suggested for the magneto-optical trap detection of CuF.

We present results of a theoretical investigation on the dynamics of the C(

We present the first accurate quantum dynamics calculations of mode-specific tunneling splittings in a sequential double-hydrogen transfer process. This is achieved in the vinylidene-acetylene system, the simplest molecular system of this kind, and by large-scale parallel computations with an efficient theoretical scheme developed by us. In our scheme, basis functions are customized for the hydrogen transfer process; a 4-dimensional basis contraction strategy is combined with the preconditioned inexact spectral transform method; efficient parallel implementation is achieved. Mode-specific permutation tunneling splittings of vinylidene states are reported and tremendous mode-specific promotion effects are revealed; in particular, the CH2 rock mode enhances the ground-state splitting by a factor of 10(3). We find that the ground-state vinylidene has a reversible-isomerization time of 622 ps, much longer than all previous estimates. Our calculations also shed light on the importance of the deep intermediate well and vibrational excitation in the double-hydrogen transfer processes.

Quasiclassical trajectory (QCT) calculations have been performed on a new global ab initio potential energy surface (PES) for the singlet ground state (1(1)A') of the CH2 reactive system. Our new PES can give a very good description of the well and asymptote regions, and particularly regions around conical intersections (CIs) and of van der Waals (vdW) interactions. The integral cross sections, differential cross sections, and product rovibrational state distributions for the C((1)D) + H2 → CH + H reaction have been investigated in a wide range of collision energies. The present integral cross sections are much larger than the previous QCT results at low collision energies, which can be attributed to the differences of the PESs in the regions around the CIs and vdW complexes. The thermal rate coefficients in the temperature range 200-1500 K have also been calculated and very good agreement with experiment is obtained.

Polybrominated diphenyl ethers (PBDEs) have received special environmental concern because of their potential toxicity to humans and wildlife worldwide. However, their photochemical degradation mechanisms remain largely unknown. Herein, a PCM/TD-DFT scheme (time-dependent density functional theory combined with the polarizable continuum model) augmented with explicit solute-solvent interactions is used to explore the promotive effects of the toluene solvent on the photochemical degradation debromination of deca-BDE (BDE209). The face-to-face π-π interactions between penta-bromine-substituted phenyl and toluene are investigated. The calculations indicate that the face-to-face π-π interaction plays an important role in the low-lying π→σ* transitions of BDE209-toluene π-stacking complex at around 300 nm in the sunlight region, which leads to notable changes for the πσ* excited states and which promotes the breaking of the C-Br bonds. The photodegradation reaction via an intermolecular charge-transfer excited state formed by the electronic transition from a π orbital of toluene to a σ* orbital of BDE209 is found to be a dominant mechanism. Our calculation results reveal the mechanism of how the participation of an explicit toluene solvent molecule catalyzes the photodegradation of BDE209 and explain the experimental results successfully. The present study may provide helpful information for the removal of PBDE contamination.

Nine doublet Λ-S states of calcium monochloride (CaCl) are calculated using the internally contracted multireference configuration interaction method with the Davidson correction. Both the core subvalence and spin-orbit coupling effects are taken into account. Laser cooling of CaCl and production of ultracold chlorine atoms are investigated and assessed. Our computed spectroscopic constants and radiative lifetimes match the available experimental data very well. The determined Franck-Condon factors and vibrational branching ratios of the A(2)Π1/2(ν('))←X(2)Σ1/2 (+)(ν) transition are highly diagonally distributed and the evaluated radiative lifetime for the A(2)Π1/2(ν' = 0) state is 28.2 ns, which is short enough for rapid laser cooling. Subsequently, detection of cold molecules via resonance enhanced multiphoton ionization to determine the final quantum state populations is discussed and the ionization energy calculated. A multi-pulse excitation scheme is proposed for producing ultracold chlorine atoms from zero-energy photodissociation of the cooled CaCl. Our results demonstrate the possibility of producing ultracold CaCl molecules and Cl atoms.

New ab initio potential energy surfaces (PESs) for the two lowest-lying singlet 11A′ and 11A′′ electronic states of CH2, coupled by the Renner-Teller (RT) effect and meant for the spectroscopic study, are presented. The surfaces are constructed using a dual-level strategy. The internally contracted multireference configuration interaction calculations with the Davidson correction, using the aug-cc-pVQZ basis set, are employed to obtain 3042 points at the lower level. The core and core-valence correlation effects are taken into account in the ab initio calculations with a modified optimized aug-cc-pCVQZ basis set for the higher-level points. The analytical representations of these PESs, with the inclusion of the nonadiabatic RT terms, are obtained by the nonlinear least-squares fit of the calculated points to three-body expansion. Quantum dynamical calculations are performed on these PESs, and the computed vibronic energy levels for the two singlet electronic states are in excellent agreement with experiment.

Polybrominated diphenyl ethers (PBDEs) have received significant environmental concern because of their potential toxicity to humans and wildlife worldwide. The photodegradation debromination of deca-BDE (BDE209) in the tetrahydrofuran (THF) solvent in the presence of furan is explored using the time-dependent density functional theory combined with the polarizable continuum model. Our calculations reveal that the lone pair–π interaction between BDE209, and THF has a significant effect on the low-lying excitation and reduces the binding energies of C–Br bonds to some extent, which accounts for the photodegradation via the π BDE209 σ* excited state and explains experiment successfully. We find that the addition of a small quantity of furan can promote the photodegradation of BDE209 in THF effectively and this is attributed to the π-stacking interaction between BDE209 and furan, which plays an important role in the low-lying π → σ* transitions in the sunlight region.

The reaction of O(3P) with 1-butene (CH3CH2CH?CH2) are examined by applying the UMP2 and G3 methods. The minimum energy crossing points (MECPs) between the singlet and triplet potential energy surfaces are located using the Newton-Lagrange method, and it is shown that the MECPs play a key role in the reaction mechanisms. The complex reaction mechanisms are revealed for both adiabatic and nonadiabatic reaction channels, and the observations in several recent experiments can be rationalized based upon the present calculations. The calculational results indicate that the site selectivity of the addition of O(3P) to either carbon atom of the double bond of 1-butene is not remarkable. In addition, the formation mechanisms of butenols are discussed. The butenols can be created not only by the keto-enol tautomerization, but also by the rearrangement and decomposition reaction involving the epoxy compound. (C) 2011 Wiley Periodicals, Inc. Int J Quantum Chem, 2011

Full-dimensional quantum dynamics calculations of vinylidene-acetylene isomerization are performed and the state-specific resonance decay lifetimes of vinylidene(-d(2)) are computed. The theoretical scheme is a combination of several methods: normal coordinates are chosen to describe the nuclear motion of vinylidene, with both the parity and permutation symmetry exploited; phase space optimization in combination with physical considerations is used to generate an efficient discrete variable representation; the reaction coordinate is defined by us according to the three most relevant normal coordinates, along which a kind of optimal complex absorbing potential is imposed; the preconditioned inexact spectral transform method combined with an efficient preconditioner is employed to extract the energies and lifetimes of vinylidene. The overall computation is efficient. The computed energy levels generally agree with experiment well, and several state-specific lifetimes are reported for the first time.

A theoretical study on various properties of the ground and first excited states of two 7-aminocoumarin dyes with heterocyclic substituents at the 3-position is presented. The ground-state and excited-state geometries were optimized at the Hartree–Fork and configuration interaction singles levels of theory, respectively. The geometric relaxation between the first excited state and the ground state was examined and explained in terms of the nodal patterns of the highest occupied and lowest unoccupied molecular orbitals. The most striking geometrical relaxation is the twisting motion between the parent coumarin and heterocyclic substituent at the 3-position. The absorption and emission wavelengths were calculated using the time-dependent density functional theory, and the solvent effect on geometries and spectra has been taken into account using the polarized continuum model. Our calculated results are in good agreement with the experimental measurements, and the influences of solvents and heterocyclic substituents on spectra are also discussed.