The Journal of Physical Chemistry A最新文献

A new method is presented for the measurement of electron inelastic mean free path (IMFP) of copper metal from the K-edge X-ray absorption fine structure (XAFS) using energies from 5 to 320 eV above the edge. The accuracy of theoretical determinations of electron IMFP at low energies is one of the key limiting factors in current XAFS modeling and Monte Carlo transport. Significant discrepancies between theoretical and experimental IMFP values have been revealed through recent studies, posing significant questions regarding the accuracy of key structural parameters extracted through XAFS analysis. Small molecules and organometallic systems, which often lack robust tabulations of key electron scattering data, are particularly susceptible to inconsistencies in the IMFP, requiring a new methodology to resolve these discrepancies. XAFS is determined using an advanced density functional theory (DFT) core of the finite difference method for XAFS (FDMX). The popular multiple-scattering approach, based on muffin-tin potentials, is shown to be inadequate for accurately calculating the fine structure. Experimental IMFP measurements are both consistent with past measurements and consistent with the latest plasmon theory. However, variation of measurements with temperature points to the need for fine spacing at room temperature and measured uncertainties of data points at low temperatures and also suggests significant temperature-dependent effects both of broadening and correlation from multiple sources. This work confirms both recent past experimental and theoretical works and points to new areas of challenge and discrepancy.

Heats of formation, bond dissociation energies, proton affinities, gas phase acidities, and pK_a values in water, dimethyl sulfoxide, acetonitrile, and tetrahydrofuran were calculated for all hydrogen-containing halomethanes and methane using composite correlated molecular orbital theory at the G3(MP2) and Feller-Peterson-Dixon (FPD) levels. Notably, the G3(MP2) method was extended to include iodine-containing compounds. The calculated gas phase acidities generally agree with available experimental data within experimental error limits, often within ±4 kJ/mol; however, CH₂F₂ is a significant exception where theory and experiment differ by nearly 40 kJ/mol for the acidity ΔG. Aqueous pK_a values range from 53.6 for CH₃F to 28.0 for CHF₂I. The latter’s unexpectedly high acidity results from the CF₂I^– anion resembling a CF₂ carbene interacting with an iodide anion. These computed values rationalize literature base choices for anion generation: trihalomethanes (pK_a 28.0–34.2) are deprotonated by nonorganometallic bases (KOH, DBU, KOtBu), whereas less acidic dihalomethanes (pK_a ≳ 38), particularly fluorodihalomethanes (pK_a 42–49), require strong metal amides (e.g., LTMP, LDA), with LHMDS proving inadequate. An experimental CHBrCl₂ case study corroborates these predictions, showing clean deprotonation with lithium amides compared to diminished efficiency with weaker bases due to competitive hydroxide addition. This work provides the most comprehensive high-accuracy thermochemical data set for the complete set of hydrogen-containing halomethanes.

We report a femtosecond time-resolved strong-field study of ammonia borane (AB, BH₃NH₃) following both single and double ionization, revealing ultrafast fragmentation dynamics and hydrogen release. Time-resolved mass spectrometry and ab initio molecular dynamics simulations are used to identify the molecular origin of the neutral and ionic products. Singly ionized AB produces neutral H and H₂, while doubly ionized AB produces neutral H and H₂ along with H⁺, H₂⁺, and H₃⁺, all within 1 ps. Electronic-structure calculations show that H, H⁺, H₂, H₂⁺, and H₃⁺ originate predominantly from hydrogen atoms bound to the boron center and that their formation proceeds through hydrogen migration and, in some channels, neutral H₂ roaming. The calculations further indicate that the dication meets the structural and energetic requirements for neutral H₂ release, a prerequisite for forming astrochemically relevant H₃⁺. However, the large adiabatic relaxation energy causes most roaming H₂ to dissociate before proton abstraction, suppressing H₃⁺ formation. These results provide new insight into dissociative ionization pathways in hydrogen-rich molecules, extend mechanistic principles developed for halogenated alkanes to ammonia borane, and suggest implications for hydrogen-release chemistry in ammonia-borane-based storage materials.

We introduce the noniterative Fermi–Löwdin orbital self-interaction correction (NIFLOSIC) method as a computationally efficient alternative to traditional Fermi–Löwdin orbital self-interaction correction (FLOSIC) by eliminating the need for iterative relaxation of Fermi orbital descriptors (FODs). This is accomplished using the selected columns of the density matrix localization scheme [J. Chem. Theory Comput. 2023, 19, 8572] and by exploiting the relationship between the electron localization function and FODs [J. Chem. Phys. 2025, 162, 144105]. The approach produces localized orbitals that are slightly more compact than grid-based selected columns of the density matrix orbitals and generates FODs in a single, noniterative self-starting step, following density functional theory calculations. Within a generalized Kohn–Sham framework, full relaxation of the density minimizes the Perdew–Zunger energy functional, yielding self-interaction corrected densities and orbitals. NIFLOSIC reproduces results from fully self-consistent FLOSIC calculations, while significantly reducing computational cost. Although the total electronic energy is not suitable for thermochemistry, benchmark tests across diverse molecular systems demonstrate that NIFLOSIC significantly improves frontier molecular orbital energies and dipole moments, establishing a practical and scalable approach for large-scale electronic structure applications where self-interaction correction is needed.

We generate an electronegativity scale based on the ability of atoms and functional groups in molecules to take electrons from the other atoms and functional groups therein. To do this, we construct the minimum weighted feedback arc set, which provides a ranking of moieties’ electronegativity based on the number of electrons they accept, or donate, from other moieties. A rating scale for electronegativity is then constructed by projecting data about the pairwise electronegativity difference onto a one-dimensional manifold. Our results are broadly in line with more traditional scales of the electronegativity and electronic chemical potential, especially Pauling’s definition.

The formation of sulfate, a major component of fine particles posing significant threats to human health, is closely linked to the speciation of Fe(III) complexes with S(IV) at the air–water interface, a crucial yet underexplored aspect of atmospheric sulfur cycling. The speciation of Fe(III)-sulfito complexes at the interface remains poorly understood and thus hinders the understanding of the oxidizing properties of transition metals in atmospheric aerosol. Here, we reveal the coordination preference of the active reaction center (Fe(III)-sulfito complex) and the ligand substitution mechanism between Fe(III)-sulfito complexes and H₂O at the air–water interface. Our results demonstrate that the Fe(III) complexes coordinated by HSO₃^– undergo a rapid and spontaneous transformation from S-coordination to O-coordination within picoseconds. Furthermore, the substitution reaction of HSO₃^– in [Fe(H₂O)₄(OH)(HSO₃)]⁺/[Fe(H₂O)₃(OH)₂(HSO₃)] by the H₂O nucleophile proceeds via both a kinetically and thermodynamically favorable pathway, characterized by free energy barriers of ∼6.39/3.81 kcal/mol. These findings further demonstrate that HSO₃^– preferentially occupies the second hydration shell of hydrolyzed Fe(III) complexes. The dynamic equilibrium between competing coordination forms provides molecular-scale insights into interfacial metal–sulfur chemistry, where distinct Fe(III) complexes govern the catalytic behavior of the system, thereby bridging coordination chemistry and atmospheric science.

The source of atmospheric nitrous acid (HONO) has not yet been fully identified, as observed concentrations remain significantly higher than predicted levels. The hydrolysis reaction of t-ONONO₂, as a feasible source of HONO, has attracted much attention in the field of atmospheric chemistry. In this study, the roles of sulfuric acid (SA), methanesulfonic acid (MSA), and methyl hydrogen sulfate (MHS) in the hydrolysis reaction of t-ONONO₂ to produce HONO and HNO₃ were explored by DFT and statistical dynamics methods. Thermodynamic and kinetic data indicate that SA, MHS, and MSA enhance the hydrolysis reaction of t-ONONO₂ through two mechanisms: single hydrogen atom transfer (S-HAT) and double hydrogen atom transfer (DHAT). Among these, SA exhibits the strongest catalytic effect. This study will contribute to a better understanding of the mechanistic characterization of t-ONONO₂ hydrolysis reactions, which is of great significance for the control of atmospheric particulate matter in polluted areas.

We investigate the photophysics of the aza-BODIPY dimer D[1,3], formed by linking two aza-BODIPY monomers by a C–C single bond at positions 1 and 3, using multireference electronic structure calculations and quantum nuclear dynamics. Our findings reveal that the dimer exhibits strong electronic couplings and weakly endoergic singlet fission (SF) energetics, making SF energetically feasible. Superexchange-like adiabatic states are obtained, giving rise to cross-correlation contributions in the simulated absorption spectrum from a localized diabatic state. Re-expressing the diabatic Hamiltonian from a local basis to a superexchange basis allowed accurate simulation of the absorption spectrum. Quantum nuclear dynamics simulations show rapid formation of a superexchange-like state on a 50 fs time scale. The formed superexchange-like state is composed of charge transfer (CT) (30%), multiexcitonic (20%), and local excitation (20%) configuration state functions (CSFs). The limited multiexcitonic character renders SF inefficient. Instead, the charge-transfer manifold becomes substantially populated, activating an alternative route for triplet formation. Spin–orbit coupling calculations and rates of intersystem crossing (10⁷ s^–1) reveal that the spin–orbit charge-transfer intersystem crossing (SOCT-ISC) mechanism provides a more effective pathway for triplet-state generation in the dimer D[1,3].

Recently we presented a new time-resolved, double-imaging photoelectron photoion coincidence (i²PEPICO) spectrometer for the study of chemical reactions using fixed frequency, single-photon vacuum ultraviolet ionization. Here we describe new capabilities and insights from this instrument when coupled with tunable ionizing radiation. We interrogate the gas expansion dynamics of a side-sampled chemical reactor tube, revealing clear evidence for viscous flow in the expansion before ionization. Cation imaging can be used to restrict detected signal to only the direct molecular beam, removing contributions from background and reflected gases. We characterize the peak shape and mass resolution of the instrument, provide new insight and clarification regarding collection efficiencies, and consider the noise sources and resulting signal-to-noise in PEPICO experiments. We quantify the temporal instrument response function and show that velocity map imaging of cations may be used to eliminate the transit time delay and reduce the temporal blurring inherent in ex situ sampling geometries. The resulting upper bound of time resolution is 7 μs, a significant improvement compared to previous instruments. We discuss methods to quantify and address the ubiquitous problem of background electrons ejected from metal surfaces in photoelectron spectrometers. Finally, we compare variants of photoion mass-selected photoelectron spectroscopy, provide an example of quantitative analysis using PEPICO, and present evidence for unexpected products in the 193 nm photodissociation of CH₃OH that underscores the value of universal imaging approaches.

New photoelectron (PE) spectra of C₆Cl_xF_6–x^– (x = 2, 3, 5) are presented and compared with previously reported PE spectra of C₆F₆^– and C₆ClF₅^–, along with the known properties of C₆Cl₆^–. Based on a recent theoretical study [J. Phys. Chem. A 2024, 128, 8072–8079], anions of the mixed perchlorofluorobenzenes have competing molecular and electronic structures: one in which the electron is localized in a single C–Cl σ* orbital, resulting in a structure with a uniquely elongated C–Cl bond, and the other in which the excess charge is more delocalized, resulting in a more symmetric anion. In all cases, the experimental PE spectra are consistent with the former, with the exception of C₆Cl₅F^–, the spectrum of which is not consistent with calculations on either structure. The adiabatic electron affinities of the neutrals are difficult to ascertain from the anion PE spectra because of vanishingly small signal near the origin. However, the vertical detachment energies are determined to be 3.20(10) eV for C₆Cl₂F₄^–, 3.09(5) eV for C₆Cl₃F₃^–, and 1.85(10) eV for C₆Cl₅F^–. The VDEs of C₆Cl₂F₄^– and C₆Cl₃F₃^– are similar to the previously reported VDE of C₆ClF₅^–, 2.95 eV [J. Phys. Chem. A 2024, 128, 5646–5658], and significantly higher than the previously reported VDE determined from the PE spectrum of C₆F₆^–, 1.60 eV, measured on the same instrument [J. Phys. Chem. A 2023, 127, 556–8565]. To further benchmark the computational methods and gain insights into the relationship between the anionic structures in which the excess charge is localized in a single C–Cl σ* orbital and the delocalized structure, we measured the PE spectrum C₂Cl₄^–, which exhibited a VDE consistent with the computed structure in which the excess charge is localized in a single C–Cl σ* orbital, and which was the computed lowest energy structure of C₂Cl₄^–. We further explore the relationship between localized and delocalized structures in this molecular anion and C₆Cl₅F^–.