Multireference Ab Initio Study of the Ground and Low-LyingExcited States of Cr(CO)2 and Cr(CO)3

We investigate the ground and low-lying excited states of unsaturated chromium carbonyls, Cr(CO)2 and Cr(CO)3, using multiconfigurational ab initio perturbation theory. Unlike other chromium carbonyls, there are discrepancies between the experiment and theory on the identity of the ground states of Cr(CO)2 and Cr(CO)3. From multireference ab initio calculations considering the full valence orbitals of Cr(CO)2 and Cr(CO)3, the differences in the molecular structures of their various electronic states are explained by the electronic structure analysis. On the basis of the result from CASPT2 and MS-CASPT2 calculations, we propose that the ground states of Cr(CO)2 and Cr(CO)3 are the 5Πg and 1A1 states, respectively, addressing the ambiguity regarding their ground states. In addition, the multiconfigurational ab initio perturbation theory calculations reveal that (1) the energy gaps between the ground and first low-lying excited states of Cr(CO)2 and Cr(CO)3 are quite small and (2) the first low-lying excited states of Cr(CO)2 and Cr(CO)3 have the same spin multiplicities as the ground states of CrCO and Cr(CO)2, respectively, which are the products of ligand dissociation. As a result, the apparent spin-forbidden dissociation of Cr(CO)2 and Cr(CO)3 into CrCO and Cr(CO)2, respectively, are likely to be facilitated by thermal excitation of the ground states of Cr(CO)2 and Cr(CO)3 into their first low-lying excited states, which then actually undergoes the spinallowed dissociation to the ground states of CrCO and Cr(CO)2 with the same spin multiplicities.1221sciescopu

Spin–Orbit Effect on the Molecular Properties of TeX_<i>n</i> (X = F, Cl, Br, and I; <i>n</i> = 1, 2, and 4): A Density Functional Theory and Ab Initio Study

Density functional theory (DFT) and ab initio calculations, including spin–orbit coupling (SOC), were performed to investigate the spin–orbit (SO) effect on the molecular properties of tellurium halides, TeX_<i>n</i> (X = F, Cl, Br, and I; <i>n</i> = 1, 2, and 4). SOC elongates the Te–X bond and slightly reduces the vibrational frequencies. Consideration of SOC leads to better agreement with experimental values. Møller–Plesset second-order perturbation theory (MP2) seriously underestimates the Te–X bond lengths. In contrast, B3LYP significantly overestimates them. SO-PBE0 and multireference configuration interactions with the Davidson correction (MRCI+Q), which include SOC via a state-interaction approach, give the Te–I bond length of TeI₂ that matches the experimental value. On the basis of the calculated thermochemical energy and optimized molecular structure, TeI₄ is unlikely to be stable. The use of PBE0 including SOC is strongly recommended for predicting the molecular properties of Te-containing compounds

Multireference Ab Initio Study of the Ground and Low-Lying Excited States of Cr(CO)₂ and Cr(CO)₃

We investigate the ground and low-lying excited states of unsaturated chromium carbonyls, Cr­(CO)₂ and Cr­(CO)₃, using multiconfigurational ab initio perturbation theory. Unlike other chromium carbonyls, there are discrepancies between the experiment and theory on the identity of the ground states of Cr­(CO)₂ and Cr­(CO)₃. From multireference ab initio calculations considering the full valence orbitals of Cr­(CO)₂ and Cr­(CO)₃, the differences in the molecular structures of their various electronic states are explained by the electronic structure analysis. On the basis of the result from CASPT2 and MS-CASPT2 calculations, we propose that the ground states of Cr­(CO)₂ and Cr­(CO)₃ are the ⁵Π_g and ¹A₁ states, respectively, addressing the ambiguity regarding their ground states. In addition, the multiconfigurational ab initio perturbation theory calculations reveal that (1) the energy gaps between the ground and first low-lying excited states of Cr­(CO)₂ and Cr­(CO)₃ are quite small and (2) the first low-lying excited states of Cr­(CO)₂ and Cr­(CO)₃ have the same spin multiplicities as the ground states of CrCO and Cr­(CO)₂, respectively, which are the products of ligand dissociation. As a result, the apparent spin-forbidden dissociation of Cr­(CO)₂ and Cr­(CO)₃ into CrCO and Cr­(CO)₂, respectively, are likely to be facilitated by thermal excitation of the ground states of Cr(CO)₂ and Cr(CO)₃ into their first low-lying excited states, which then actually undergoes the spin-allowed dissociation to the ground states of CrCO and Cr­(CO)₂ with the same spin multiplicities

Experimental Study on Ion Transport in Microfluidic Electrodialysis Using Partially Masked Ion Exchange Membranes

Electrodialysis using anion-exchange membranes (AEMs) and cation-exchange membranes (CEMs) has been widely used for water desalination and the management of various ionic species. During commercial electrodialysis, the available area of an ion-exchange membrane is reduced by a non-conductive spacer that is in contact with the AEM/CEM. Although multiple reports have described the advantages or disadvantages of spacers, fewer studies have explored the effects of spacers on the mass transport effect of the reduced membrane area excluding the fluid flow change. In this paper, we present our experimental studies concerning mass transport in microfluidic electrodialysis systems with partially masked ion-exchange membranes. Six different types of masking membranes were prepared by the deposition of non-conductive films on parts of the membranes. The experimental results showed that the overlapped types (in which masking was vertically aligned in the AEM/CEM) exhibited a larger electrical conductance and better current/energy efficiency, compared with the non-overlapped types (in which masking was vertically dislocated in the AEM/CEM). We also observed that a reduction in the unit length of the unmasked ion-exchange membrane enhanced overall mass transport. Our results demonstrate the effects of patterned membranes on electrical resistance and desalination performance; they also identify appropriate arrangements for electromembrane systems

Ab Initio Analysis of Auger-Assisted Electron Transfer

Quantum confinement in nanoscale materials allows Auger-type electron–hole energy exchange. We show by direct time-domain atomistic simulation and analytic theory that Auger processes give rise to a new mechanism of charge transfer (CT) on the nanoscale. Auger-assisted CT eliminates the renown Marcus inverted regime, rationalizing recent experiments on CT from quantum dots to molecular adsorbates. The ab initio simulation reveals a complex interplay of the electron–hole and charge–phonon channels of energy exchange, demonstrating a variety of CT scenarios. The developed Marcus rate theory for Auger-assisted CT describes, without adjustable parameters, the experimental plateau of the CT rate in the region of large donor–acceptor energy gap. The analytic theory and atomistic insights apply broadly to charge and energy transfer in nanoscale systems

Prospect of Retrieving Vibrational Wave Function by Single-Object Scattering Sampling

The exact shape of wave functions has never been directly measured because an ensemble measurement is often overwhelmed by the contributions of highly populated configurations. In this work, we explore the possibility of directly obtaining vibrational wave functions by single object scattering sampling (SOSS) using intense, ultrashort X-ray pulses provided by X-ray free electron lasers. Previously, single molecule diffraction experiments using femtosecond X-ray pulses have been proposed with the prospect of determining three-dimensional structure of macromolecules without the need of single crystal samples. In contrast to the previous proposals, SOSS is designed for obtaining the structural variations of constantly fluctuating molecules by sampling many single shot, single object scattering patterns From the simulations on iodine molecules adopting various pulse characteristics and molecular parameters, we were able to reconstruct vibrational wave functions of molecular iodine and found that SOSS is feasible under appropriate experimental conditions.112sciescopu

Mechanistic Investigation of Thermal and Photoreactions between Boron and Silane

Density functional theory and high-level ab initio calculations were performed to elucidate the detailed reaction mechanism from B and SiH₄ to a structure with two bridging H atoms (Si­(μ-H₂)­BH₂, silicon tetrahydroborate). On the basis of the calculated results, this reaction mechanism includes both thermal and photochemical reactions. Especially, thermal conversion of silylene dihydroborate (H₂BSiH₂) to Si­(μ-H₂)­BH₂ is not feasible because two high energetic barriers must be overcome. In contrast, the reverse reaction is feasible because it is effectively only necessary to overcome a single barrier. The characteristics of the excited states of H₂BSiH₂ and Si­(μ-H₂)­BH₂ have been identified. Two successive conical intersections (CIs) are involved in the photochemical reaction. The BSiH₄ bending coordinate is almost parallel to the reaction coordinate near the regions from the second CI to Si­(μ-H₂)­BH₂. The activated BSiH₄ bending mode lift the degeneracy of the second CI, thereby the reaction readily proceeds to Si­(μ-H₂)­BH₂. All calculated results in this work reasonably well describe the recent experimental observations

Reactivity of molecular oxygen with aluminum clusters: Density functional and Ab Initio molecular dynamics simulation study

Dissociative adsorption of molecular oxygen (O-2) on aluminum (Al) clusters has attracted much interest in the field of surface science and catalysis, but theoretical predictions of the reactivity of this reaction in terms of barrier height is still challenging. In this regard, we systematically investigate the reactivity of O-2 with Al clusters using density functional theory (DFT) and atom-centered density matrix propagation (ADMP) simulations. We also calculate potential energy surfaces (PESs) of the reaction between O-2 and Al clusters to estimate the barrier energy of this reaction. The M06-2X functional gives the barrier energy in agreement with the one calculated by coupled cluster singles and doubles with perturbed triples (CCSD(T)) while the TPSSh functional significantly underestimates the barrier height. The ADMP simulation using the M06-2X functional predicts the reactivity of O-2 with the Al cluster in agreement with the experimental findings, that is, singlet O-2 readily reacts with Al clusters but triplet O-2 is less reactive. We found that the ability of a DFT functional to describe the charge transfer appropriately is critical for calculating the barrier energy and the reactivity of the reaction of O-2 with Al clusters. The M06-2X functional is relevant for investigating chemical reactions involving Al and O-2. (c) 2016 Wiley Periodicals, Inc.11Nsciescopu

Ab Initio Investigation of the Ground States of F₂P(S)N, F₂PNS, and F₂PSN

A recent spectroscopic experiment identified difluorothiophosphoryl nitrene (F₂P­(S)­N) and found that it showed rich photochemistry. However, a discrepancy between the experimental results and the quantum chemical calculations was reported. Thus, high-level ab initio calculations using the coupled cluster singles and doubles with perturbative triples and second-order multiconfigurational perturbation theory were performed to elucidate this inconsistency. The discrepancy arose due to the failure to consider the triplet state of difluoro­(thionitroso)­phosphine (F₂PNS). In this work, we identify that the global minimum of the system is the triplet state of F₂PNS, which allows us to explain the inconsistency between the experimental and theoretical results. All calculated results give consistent results with the recent experimental results

Self-Piercing Riveted Joint of Vibration-Damping Steel and Aluminum Alloy

In this study, the self-piercing rivet (SPR) joining of vibration-damping steel and aluminum alloy (Al5052-H32) is successfully carried out, for the first time to our knowledge, and the effects of die type and joint configuration on the mechanical performance, failure mode, and geometrical characteristics of the new joint are investigated. The vibration-damping steel and Al5052-H32 SPR joint exhibits the largest tensile&ndash;shear load when a flat die is used. An increase in the die taper angle and diameter decreases the mechanical performance of the joint due to the increase in volume of the die, leading to a smaller interlock width of the joint. The joint configuration with Al5052-H32 as a top sheet has superior mechanical performance compared with the reverse configuration, owing to the increase of the interlock width. All SPR joints of vibration-damping steel and Al5052-H32 show consistent rivet pull-out failure, regardless of the joint configuration, because of relatively small interlock width. It is also found that these SPR joints show better mechanical performance than those of SPFC590DP (a skin material of the vibration-damping steel) and Al5052-H32 under the Al5052-H32&ndash;top configuration