The Journal of Physical Chemistry A最新文献

We obtained the photoelectron spectra of Rh(CN)^- using the negative ion photoelectron velocity-map imaging (NI-PEVMI) technique and revealed the photodesorption process of Rh(CN)^-. The vertical detachment energy (VDE) and adiabatic detachment energy (ADE) of Rh(CN)^- have both been experimentally reported to be 2.04 (3) eV. The Franck-Condon (FC) simulation of the ground state of Rh(CN)^- was conducted to facilitate a more accurate identification of the experimental photoelectron spectra. The existence of isomer Rh(NC)^- was confirmed by the FC simulation result. The vibration frequencies of Rh(CN) and Rh(NC) measured by photoelectron spectroscopy are 462 (50) cm^-1 and 471 (50) cm^-1, respectively. Based on density functional theory, the stable geometries of Rh(CN)_n^-1/0 (n = 1-3) clusters were obtained, the values of VDEs and ADEs were calculated, and the photoelectron spectroscopy (PES) was simulated. These can provide theoretical guidance for the experimental study of rhodium cyanide complexes in the future. Finally, we also conduct molecular orbital analysis, natural population analysis, natural resonance theory, and electron localization function analysis to further reveal the nature of the interaction between transition metal Rh and (CN)_n ligand. Through the study of Rh(CN)_n^-1/0 (n = 1-3) complexes, it is found that the transition metal rhodium (Rh) is more inclined to cyanide arrangement.

We present a new theory for partitioning simulations of periodic and solid-state systems into physically sound atomic contributions at the level of Kohn-Sham density functional theory. Our theory is based on spatially localized linear combinations of crystalline Gaussian-type orbitals and, as such, capable of exposing local features within periodic electronic structures in a more intuitive and robust manner than alternatives based on the spatial distribution of atomic basis functions alone. Early decomposed cohesive energies of both molecular polymers and different crystalline polymorphs demonstrate how the atomic properties yielded by our theory convincingly align with the expected charge polarization in these systems, also whenever partial charges and Madelung energies may lend themselves somewhat ambiguous to interpretation.

A synergetic study that utilized anion photoelectron spectroscopy and high-level ab initio calculations has explored the activation of H₂O molecules by ThO₂^- molecular anions. Both experiment and theory found conclusive evidence for said activation. In the experiments, this appeared as a tell-tale directional shift in the spectral profile of the anionic complex that ruled out physisorption, i.e., ThO₂^-(H₂O), and implied chemisorption. In the computations, good agreement was found between the calculated and measured vertical detachment energies, and the atomic connectivity (the structure) of the resulting anionic complex was found to be [OTh(OH)₂]^-.

The high resolution ro-vibrational spectrum of the diatomic molecule vanadium oxide (VO) in the gas phase was measured around 1000 cm^-1. In total, 1529 ro-vibrational transitions were assigned, in a spectral range of 984-1036 cm^-1. For many transitions, the hyperfine structure resulting from the nuclear spin of ⁵¹V were resolved and the molecular parameters for the first (v = 1) and second (v = 2) excited vibrational state of VO were derived. The molecules were generated using a laser ablation source in which a vanadium rod was laser ablated and gaseous nitrous oxide (N₂O) was introduced, as an oxygen donor. Subsequent supersonic adiabatic expansion cooled the molecules. The spectrum of VO was measured with quantum cascade lasers where the laser beams were perpendicularly oriented to the supersonic jet.

Energetic ionic liquids have a high potential to replace the traditional monopropellant hydrazine as a high-energy green propellant and can be widely used in aerospace technology. A high-energy ionic liquid─HEHN has also gained extensive attention from researchers. To explore the reaction mechanism of HEHN and establish a chemical kinetic model for high-energy ionic liquid propellants, 28 hydrogen abstraction reactions of HEH, which is the main decomposition product of HEHN, were investigated in this study. Seven abstractors were involved, including ^•H, ^•OH, NO₂, HO₂^•, ^•CH₃, CH₃O^•, and CH₃O₂^•. In the case of ab initio calculations, the M06-2X/6311++G(d,p) approach was utilized for geometry optimization, determination of vibrational frequencies, and dihedral scans. The CCSD/cc-pVXZ (X = T, Q) level of theory was used to calculate the single-point energies (SPEs). The rate coefficients of all 28 reactions and the thermochemical parameters of all involved species were determined. The results indicate that the rate of hydrogen abstraction at the -NH site is faster than that at other sites at relatively low temperatures. For all four abstraction sites, HEH + ^•H, ^•OH, and CH₃O^• have higher reaction rates than HEH + CH₃O₂^• and HO₂^•. In particular, NO₂ systems at the -NH and -NH₂ sites even begin to show higher reactivity than the ^•H, ^•OH, and CH₃O^• systems when the temperature is above ∼1100 K.

The hydrogen abstraction reactions by small radicals from fuel molecules play an important role in the oxidation of fuels. However, experimental measurements and/or theoretical calculations of their rate constants under combustion conditions are very challenging due to their high reactivity. Machine learning offers a promising approach to predicting thermal rate constants. In this work, three machine learning methods, XGB, FNN, and XGB-FNN hybrid algorithms, were employed to train and predict the rate constants of the hydrogen abstraction reactions between alkanes and OH/HO₂. Six descriptors were selected according to the Pearson correlation coefficients, the importance of descriptors, and the clustering heat map. It was proven that the XGB-FNN model is the most robust. The constructed XGB-FNN model achieved an average deviation of 89.13% for the alkanes + OH reactions and 190.93% for the alkanes + HO₂ reactions on their respective prediction sets. The model was also used to predict the rate constants of the reactions involving larger alkanes, demonstrating its extrapolation capability. Furthermore, the model has the ability to distinguish the reactivity of the reactions with the hydrogen atom abstracted at different sites of alkane.

Highly energetic boron (B) particles embedded in hydroxyl-terminated polybutadiene (HTPB) thermosetting polymers represent stable solid-state fuel. Laser-heating of levitated B/HTPB and pure HTPB particles in a controlled atmosphere revealed spontaneous ignition of B/HTPB in air, allowing for examination of the exclusive roles of boron. These ignition events are probed in situ via simultaneous spectroscopic diagnostics: Raman and infrared spectroscopy, temporally resolved high-speed optical and infrared cameras, and ultraviolet-visible (UV-vis) spectroscopy. The emission spectra unravel two stages of the B/HTPB ignition─the exoergic ignition of boron followed by HTPB combustion. It was found that HTPB readily absorbs the energy from the irradiating carbon dioxide (CO₂) laser but efficiently transfers that thermal energy to the densely arranged boron particles due to the lower heat capacity of the latter. This transferred energy causes a surge in temperature for the boron particles, leading to ignition (in an oxygen environment) in B/HTPB, unlike the case with HTPB alone. The accumulated energy from the second stage of boron ignition triggers the decomposition of HTPB in conjunction with hydrogen abstraction to produce radical precursors via boron oxides (BO and BO₂)─the key emitting intermediates detected. Along with conventional combustion products such as carbon dioxide (CO₂) and water (H₂O), the formation of partially oxidized gaseous products such as methanol (CH₃OH) and methyl vinyl ether have also been detected as a tracer of diverse oxidation events, suggesting a complex oxidation chemistry within HTPB and overall depict crucial insights for its use as a solid rocket fuel.

The spectroscopic and dynamic properties of methyl ferulate─a naturally occurring ultraviolet-protecting filter─and microsolvated methyl ferulate have been studied under molecular beam conditions using resonance-enhanced multiphoton ionization spectroscopy in combination with quantum chemical calculations. We demonstrate and rationalize how the phenyl substitution pattern affects the state ordering of the lower excited singlet state manifold and what the underlying reason is for the conformation-dependent Franck-Condon (FC) activity in the UV-excitation spectra. Studies on microsolvated methyl ferulate reveal potential coordination sites and the influence of such coordination on the spectroscopic properties. Our quantum chemical studies also enable us to obtain a quantitative understanding of the dominant excited-state decay routes of the photoexcited ππ* state involving a ∼3 ns intersystem crossing pathway to the triplet manifold─which is much slower than found for coumarates─and a relatively fast intersystem crossing back to the ground state (∼30 ns). We show that a common T₁/S₀ crossing can very well explain the observation that T₁ lifetimes are quasi-independent of the phenyl substitution pattern.

This study investigates the equilibrium geometries of four different Se₄ isomers using the coupled cluster single and double perturbative (CCSD(T)) method, extrapolating to the complete basis sets. The ground-state geometry of the Se₄ isomer with the C_2v structure (2.8715 Å, 2.1750 Å, and 88.4°) is found to be very close to other theoretical values (2.910 Å, 2.224 Å, and 90.0°) for the Se═Se and Se-Se bond lengths and valence angle. Additionally, the adiabatic electron affinity, vertical electron affinity, and vertical ionization energy are calculated. The multireference configuration interaction method was used to calculate transitions from the singlet ground state to some excited counterparts, including the vertical excitation energy, oscillator strength, and main electronic configuration. The predicted wavelengths of electronic transitions to 1¹B_u, 1¹A_u with C_2h symmetry, and 1¹B₁ state with the C_2V symmetry could match the experimental NIR absorption band at 710-850 nm. These transitions and electronic properties may provide insights into the role of selenium in astrophysical environments, where ⁷⁴Se in the solar system has been confirmed to originate from the supernova explosion process. The theoretical results offer a deeper understanding of Se₄ electronic and geometric structures while also providing crucial spectroscopic data that could aid in the identification of selenium-containing molecules in extraterrestrial environments.