Journal of Chemical Physics最新文献

Two-dimensional (2D) perovskites have attracted considerable attention as promising candidates for optoelectronic devices due to their excellent optical properties, structural tunability, and intrinsic quantum well architectures. Understanding how phase composition regulates ultrafast carrier dynamics is essential for optimizing device performance. In this work, monocrystalline thin films of (PEA)2(MA)n-1PbnI3n+1 with well-controlled phase distributions were prepared using a space-confined anti-solvent crystallization method. Micro-area femtosecond pump-probe spectroscopy was employed to investigate the influence of phase composition on the relaxation behavior of photoexcited carriers. The results reveal that increasing the proportion of small-n phases leads to a pronounced extension of the excited-state relaxation process in large-n domains, attributed to suppressed defect-assisted trapping and enhanced interphase carrier transfer efficiency. This study provides a microscopic physical picture of the energy funneling mechanism governed by phase composition in quasi-2D perovskites and establishes an experimental framework for regulating carrier dynamics.

Chlorosomes are the antennae of the efficient light harvesting complex in green (non-sulfur) bacteria. The ultrafast energy transfer process in natural light harvesting systems can be understood in terms of exciton transport. In chlorosomes, excitons can be delocalized over hundreds of molecules, making it of eminent interest to study large model systems composed of many (thousands) of molecules that are large enough to describe the exciton dynamics that occur in vivo in chlorosomes. In this study, we examine a recently developed Frenkel exciton Hamiltonian of a three coaxial tube chlorosome model based on an all-atom molecular dynamics simulation. We use the computationally efficient time domain Förster resonant energy transfer method to find the timescales of incoherent transfer between the chlorosome walls in this large model. We found that the population transfer rate between neighboring chlorosome walls is ∼2.3 ps-1. We used three different choices of initial quantum states for these transfer processes and found that this transfer timescale between neighboring walls does not vary significantly for these.

The boron methylene (BCH2) free radical has never been identified spectroscopically. We have undertaken a series of ab initio calculations to predict the molecular structures, vibrational frequencies, and energies of the ground and first three electronically excited states of BCH2 and its various isomers and isotopologues. In the ground state, we find that the global minimum is linear HBCH, with C2v BCH2 roughly 3935 cm-1 higher and the unstable CBH2 species is a C2v weakly bound structure at 16 384 cm-1, which readily isomerizes to the linear radical. HBCH and BCH2 are separated by a large isomerization barrier (12 825 cm-1), so it may be possible to prepare boron methylene in the gas phase and detect it with spectroscopic methods. The vibrational frequencies and rotational constants of four ground-state isotopologues of BCH2 have been calculated as an aid to future IR matrix isolation and gas-phase microwave studies. Similar calculations are reported for the ground-state linear HBCH species and its cis- and trans-bent excited states. The C̃2B2-X̃2A1 electronic transition in the 320-290 nm region is the only viable option for detecting BCH2 by gas-phase absorption or laser-induced fluorescence techniques. Franck-Condon simulations of the C̃-X̃ absorption and the allowed C̃-X̃ and C̃-B̃ emission transitions have been done for 11BCH2 and 11BCD2. In addition, the rotational structure expected for the 0-0 bands of both isotopologues under supersonic expansion conditions has been simulated. The ab initio data and predicted spectra should be invaluable for attempts to identify the boron methylene free radical in the gas phase.

A new way is invented for computing Coulomb interactions in molecular dynamics simulations, which works well for bulk phase and lamina systems. This direct summation (DS) or cell dipole approach is an extension of the "Evjen" method, which was explored in the 1960s. The DS method is the Evjen method with a unit cell dipolar correction and is cast entirely in real space, involving summing the original point charge r-1 interactions, which are truncated on a unit cell basis rather than spherically for the individual point charge interactions. The theory of the DS method is extended to encompass noncubic unit cells periodic in all three Cartesian directions. For moderately sized systems, the DS method performs with comparable accuracy and computational efficiency to that of the Ewald method, both of which are formally exact. The corresponding treatment is made for a lamina system where the charges are in 3D but the unit cells are only periodic in two of the three Cartesian directions. The DS method has no adjustable parameters and is relatively straightforward to implement in existing computer codes that do not include Coulomb interactions, unlike the Ewald method.

Collision-induced autoionizing excited states play an important role in plasma formation through associative ionization, where excited states lie in resonance with the continuum. In this work, we compute the autoionization widths of various doubly excited states of the N2 molecule using equation-of-motion coupled-cluster theory combined with complex basis functions. This study represents the first application of spin-flip methods to doubly excited autoionizing states, enabled by a newly developed computational protocol based on Kaufmann basis functions. We apply this protocol to N2 and determine the widths of the Σg+3, 3-43Πu, and 23Δg states, which are potential contributors to the associative ionization process. Our results establish the complex basis function-based spin-flip method as a reliable and systematically improvable approach for resonance width calculations, opening avenues for its application to a broader class of autoionizing states in molecular systems.

The dynamics of polar and nonpolar molecules colliding with an aqueous surface are characterized by scattering molecular beams of deuterated methane and ammonia, CD4 and ND3 (Ei = 28.9 and 30.3 kJ mol-1, respectively), from a flat liquid jet of cold salty water (8 m LiBr, 230 K). Translational energy distributions of scattered species collected as a function of collision geometry probe both impulsive scattering (IS) and thermal desorption (TD) mechanisms. We find that CD4 scattering is dominated by IS and exhibits a super-specular angular distribution. The fraction of TD scattering events is notably smaller for cold salty water than for dodecane, consistent with a higher free energy of solvation for CD4 in the water jet. In contrast, no scattering signal is seen for ND3 from the water jet, a result attributed to the high solubility and efficient protonation of ND3 in liquid water. The IS channel for CD4 was analyzed using a soft-sphere model, yielding a higher internal energy (Eint) and lower effective surface mass (meff) than was seen for Ne/water; the higher value of Eint is attributed to rotational excitation of the scattered CD4. These findings demonstrate that the outcomes of a gas-liquid collision-scattering trajectory, surface adherence, and energy transfer-are directed at the molecular level by both the gaseous scatterer and liquid surface.

The magnetic molecular interferometer (MMI) is a molecular beam scattering apparatus, which allows the polarization of the rotational angular momentum (J) of ortho-H2 molecules to be controlled using tunable magnetic fields before they collide with a surface, and their J' polarization to be determined after the collision. In the current work, quantum population distribution functions, or "stereodynamical portraits," are used to visualize the rotational angular momentum polarization of ortho-H2 molecules that the MMI creates before the collision with the surface, revealing that the sensitivity of the MMI to stereodynamic effects which depend on the orientation of J with respect to the surface normal can be increased by manipulating the H2 molecules with two perpendicular magnetic fields rather than just a single field. They can also be used to depict the polarization dependence of a H2-surface collision, as shown by the example considered here, where it is found that when H2 molecules undergo diffractive scattering from a Cu(511) surface, different J polarizations are selected to scatter into different diffraction channels, just as different polarizations of J' are created after scattering. Signals measured with the MMI are necessarily dependent on both the rotational polarization the MMI creates and the dependence of the molecule-surface collision on this, and it is demonstrated that for flux detection measurements it would be possible to analyze the data directly in terms of the polarization moments which characterize these two properties to gain a more immediate insight into the stereodynamics of the collision than is possible using alternative analysis methods.

We report detailed characterization of the vibronic interactions between the first two electronically excited states, à and B̃, in SrOPh (Ph = phenyl, -C6H5) and its deuterated counterpart, SrOPh-d5 (-C6D5). The vibronic interactions, which arise due to non-adiabatic coupling between the two electronic states, mix the B̃,ν0 state with the energetically close vibronic level, Ã,ν21ν33, resulting in extra transition probability into the latter state. This state mixing is more prominent in the deuterated molecule because of the smaller energy gap between the interacting states. We model the mixing of the à and B̃ states using the Köppel-Domcke-Cederbaum (KDC) Hamiltonian parameterized in the diabatic framework of Ichino, Gauss, and Stanton on the basis of equation-of-motion coupled-cluster calculations. The simulation attributes the observed mixing to a second-order effect mediated by linear quasi-diabatic couplings between the Ã-C̃ and B̃-C̃ states. Based on the measured spectra, we deduce an effective coupling strength of ∼0.5 cm-1. Non-adiabatic couplings between different electronic states are an important factor that should be considered in the design of laser-cooling protocols for complex molecules.

Low-energy electron attachment to molecules often leads to the formation of shape resonances, which play a pivotal role in electron-driven chemical processes. While the total decay width of a resonance determines its auto-detachment lifetime, decomposing this width into partial contributions from various auto-detachment continuum channels may provide a deeper insight into the underlying decay dynamics. In this work, we explore the applicability of using bound state methods, in particular the analytic-continuation based stabilization method, for determining partial widths in medium-sized organic molecules. Angular momentum-resolved partial widths can be obtained by placing diffuse functions at the molecular center of mass. Using the stabilization method combined with the equation-of-motion electron attachment coupled cluster method, we applied this technique to pyridine and uracil, two prototypical π-conjugated systems, and analyzed the contributions of s-, p-, d-, f-, g-, h-, and i-type functions to the widths of shape resonances. Our results show that the dominant angular momentum component of each resonance width correlates strongly with the nodal structure of the corresponding resonant orbital. Importantly, we find that higher angular momentum functions, particularly d, f, g, and h, play a decisive role in accurately capturing resonance widths. Compared to conventional atom-centered augmentation schemes, the center of mass-based approach alleviates some of the uncertainties in the stabilization method associated with inconsistent avoided crossings.

In this combined experimental and theoretical work, we present state-of-the-art liquid jet experiments based on x-ray emission spectroscopy of the [Fe(CN)6]4- and [Fe(CN)6]3- molecular ions in the hard-x-ray energy range. The ab initio simulations of the valence-to-core and Kβ spectra reveal insights into the valence and metal's d-shells, respectively. These results open new perspectives for applying spectroscopy to organometallic complexes in order to disentangle and probe various environmental effects, including solvent interactions, pH variations, and ligand field influences and dynamical processes, such as charge transfer or photoinduced ligand exchange reactions such as photoaquation in solution.