The Journal of Physical Chemistry A最新文献

The rate coefficients for the reactions for XO (XO, X = Cl, Br, I) + isoprene were calculated using the RRKM and ILT approach in master equation simulation (MESMER) in the temperature range of 200-400 K at 1 atm pressure. The thermochemical and energy parameters for ClO + isoprene were calculated using the CCSD(T)/aug-cc-pVDZ//B3LYP/6-31g(2df,p) theory. In the case of the BrO and IO radical reaction, all thermochemical parameters were calculated using CCSD(T)/AVDZ//M06-2X/AVDZ (AVDZ = aug-cc-pVDZ for C, H, and O atoms and aug-cc-pVDZ-pp for the Br atom with effective core potential (ECP) approximation) and CCSD(T)/AVDZ_ecp//M06-2X/AVDZ_ecp (AVDZ_ecp = aug-cc-pVDZ for C, H, and O atoms and Def2SVP for I atom with ECP), respectively. The rate coefficient for the reaction ClO + isoprene was calculated as k(T)_200-400 K^ClO+isoprene = (3.63 ± 0.35) × 10^-13 exp - (32.5 ± 30.2)/T cm³ molecule^-1 s^-1 at 1 atm. The rate coefficients for isoprene + BrO and isoprene + IO were calculated in the temperature range of 200-400 K at 1 atm as k(T)_200-400 K^BrO+isoprene = (2.33 ± 0.07) × 10^-13 exp(431.8 ± 8.1)/T cm³ molecule^-1 s^-1 and k(T)_200-400K^IO+isoprene = (5.71 ± 0.12) × 10^-13 exp(678.8 ± 6.2)/T cm³ molecule^-1 s^-1. The rate coefficients measured for BrO and IO radicals show a negative temperature dependence over 200-400 K.

Machine learning potential has become increasingly successful in atomistic simulations. Many of these potentials are based on an atomistic representation in a local environment, but an efficient description of nonlocal interactions that exceed a common local environment remains a challenge. Herein, we propose a simple and efficient equivariant model, EquiREANN, to effectively represent a nonlocal potential energy surface. It relies on a physically inspired message-passing framework, where the fundamental descriptors are linear combinations of atomic orbitals, while both invariant orbital coefficients and the equivariant orbital functions are iteratively updated. We demonstrate that this EquiREANN model is able to describe the subtle potential energy variation due to the nonlocal structural change with high accuracy and little extra computational cost than an invariant message passing model. Our work offers a generalized approach to create equivariant message-passing adaptations of other advanced local many-body descriptors.

A chlorine-substituted Criegee intermediate, ClCHOO, is photolytically generated using a diiodo precursor, detected by VUV photoionization at 118 nm, and spectroscopically characterized via ultraviolet-visible (UV-vis)-induced depletion of m/z = 80 under jet cooled conditions. UV-vis excitation resonant with a π* ← π transition yields a significant ground state depletion, indicating a strong electronic transition and rapid photodissociation. The broad absorption spectrum peaks at 350 nm and is attributed to contributions from both syn (∼70%) and anti (∼30%) conformers of ClCHOO based on spectral simulations using a nuclear ensemble method. Electronic structure theory shows significant differences in the vertical excitation energies of the two conformers (330 and 371 nm, respectively) as well as their relative stabilities in the ground and excited electronic states associated with the π* ← π transition. Natural bond orbital analysis reveals significant and nonintuitive nonbonding contributions to the relative stabilities of the syn and anti conformers.

Decay processes of exciplexes of cyanoanthracenes with alkylbenzene donors were compared to those with alkoxybenzenes. For the three decay processes of exciplexes, the radiative rate constant (k_f) of alkoxy derivatives is slightly lower than those of alkylbenzenes at the same average exciplex energy. However, the corresponding deactivation rate constants, intersystem crossing (k_isc) and nonradiative decay (k_nr), are considerably higher. Consequently, the fluorescence quantum yields of the alkoxybenzene exciplexes are one-half to one-fifth of the corresponding alkylbenzenes at comparable emission energies. This trend is solvent-independent. The results can be rationalized in terms of the differing electronic character of the donor radical cation moieties in the alkoxy- vs alkylbenzene exciplexes and differences in their reorganization energies. The impact of these results for the design of exciplexes that emit more efficiently is discussed.

We introduce the electron attachment equation-of-motion pair coupled cluster doubles (EA-EOM-pCCD) ansatz, which allows us to inexpensively compute electron affinities, energies of unoccupied orbitals, and electron attachment spectra. We assess the accuracy of EA-EOM-pCCD for a representative data set of organic molecules for which experimental data are available, as well as the electron attachment process in uranyl dichloride. EA-EOM-pCCD provides more reliable energies for electron attachment properties than its ionization potential EOM counterpart. The advantage of EA-EOM-pCCD is demonstrated for rylene and rylene diimide units of different chain lengths, where it outperforms the more elaborate EOM-DLPNO-CCSD flavors, reducing errors by an order of magnitude.

In molecular beam scattering experiments, an important technique for measuring product energy and angular distributions is velocity map imaging following photoionization of one or more scattered species. For studies with cold molecular beams, the ultimate resolution of such a study is often limited by the product detection process. When state-selective ionization detection is used, excess energy from the ionization step can transfer to kinetic energy in the target molecular ion-electron pair, resulting in measurable cation recoil. With state-of-the-art molecular beam technology, velocity spreads as small as a few m/s are possible, thus a suitable product detection scheme must be not only highly sensitive, state-selective, and background-free, it must also produce significantly less cation recoil than the velocity spread of the molecular beams undergoing cold collisions. To date this has only been possible with the NO molecule, and our goal here is to extend this minimal-recoil capability to the fully deuterated ammonia molecule, ND₃. In this article a resonance enhanced multi photon ionization (REMPI) detection scheme for ND₃ is presented that imparts sufficiently low recoil energy to the ions, allowing, for the first time, high-resolution imaging of ND₃ collision products in cold molecule scattering experiments with HD. The excitation step of the 1 + 1' REMPI scheme requires vacuum ultra-violet (VUV) photons of ∼160 nm, which are generated through four-wave-mixing in Xe. We varied the wavelength of the second, ionization step between 434 and 458 nm, exciting ND₃ to a wide range of autoionizing neutral states. By velocity mapping the photoelectrons resulting from the detection scheme, it was possible to fully chart the ion recoil across this range with vibrational resolution for the final ionic states. Additionally, rotational resolution in the photoionization dynamics was achieved for selected excitation energies near one of the vibrational thresholds. Many of the peaks in the spectrum of autoionizing Rydberg states are assigned to specific Rydberg series using a simple Rydberg formula model.

O₂⁺ cation, as one of the major gas components in the near space environment, has attracted significant attention due to its spectroscopic properties. In this study, we systematically investigate the spectroscopic properties of the O₂⁺ cation using ab initio methods. The potential energy curves and transition dipole moments of O₂⁺ were obtained using the icMRCI + Q method combined with the ACV5Z-DK basis set. Subsequently, the vibrational and rotational energy levels, as well as the corresponding spectroscopic constants for both ground and excited states, were determined by solving the one-dimensional radial Schrödinger equation. Based on the vibrational and rotational energy levels of bound electronic states, the internal partition function of O₂⁺ was computed over the temperature range of 100-10,000 K. Utilizing the precise potential energy functions, transition dipole moment functions, and internal partition functions, the line intensities for the First Negative Band System (a⁴Π_u-b⁴Σ_g^-) and the Second Negative Band System (X²Π_g-A²Π_u) were calculated. For the first negative band system, the spectral line intensity of Δν = 1 is maximized at temperatures ranging from 100 to 7000 K. In the case of the second negative band system, the strongest vibrational band shifts with increasing temperature. We also discuss the impact of temperature on spectral lines; at higher temperatures, a greater number of energy levels are populated, allowing for the observation of more spectral lines. These findings are significant for understanding the spectral behavior of high-temperature nonequilibrium plasmas and their role during spacecraft reentry, providing a theoretical basis for experimental research.

The conjugate-pair molecules of CO and CPt provide a prototype of the autogenic isolobal relationship between the O and Pt atoms that can rationalize the structure and reactivity trends of platinum carbides. Herein, the photoelectron detachment at 532 nm has been recorded for the gas-phase CPt^- by using the photoelectron velocity-map imaging spectroscopy. The vibrationally resolved ground-state transition reveals a wealth of information concerning the electronic ground states of CPt^0/-1. Although the triple bonding characters in both CPt and CO have fortified the autogenic isolobal relationship between O and Pt, further detailed bonding comparisons have revealed the subtle nuance in the triple bonding. The triple bonds of CO comprise one σ donor bond from the O atom to the C atom and two degenerate π electron-sharing bonds. In contrast, the triple bonds of CPt involve three dative bonds, including one σ donor bond from the C atom to the Pt atom and two degenerate π back-donation bonds from the Pt atom to the C atom.

Laser-induced crystallization through optical trapping offers precise and spatiotemporal control of crystallization kinetics at the microscale region. Here, we demonstrate the optical trapping-induced crystallization of various amino acids, including glycine, l-cysteine, and l-alanine, by focusing a 532 nm continuous-wave laser in amino acid/H₂O solution. The coordinated effect of optical forces and heat-driven molecular delivery improves the local molecular concentration, leading to nucleation and subsequent crystal growth. In situ Raman spectroscopy is employed to investigate the crystallization kinetics and distinguish the crystalline phase. Orthorhombic and monoclinic crystals of l-cysteine are obtained without changing the laser polarization. Further, laser-driven crystal dissolution was observed in the absence of the interface with the morphology evolution recorded. Our work provides an all-optical strategy to control and investigate the crystallization kinetics of amino acids and can be potentially extended to other molecular systems.

n-Dodecane(C₁₂H₂₆) is a typical surrogate fuel for aviation kerosene used in high-performance aero engines. The combustion kinetics of n-dodecane at temperatures above the critical point condition is the focus of attention in the aerospace field. In this paper, the first-principles molecular dynamics method is used to study the high-temperature oxidation of C₁₂H₂₆. Before C-C bond dissociation, C₁₂H₂₆ is oxidized to form oxidized C₁₂ species containing multiple C═O, -OH, -O-, and -COOH groups, while releasing a large amount of energy. In addition, before the C-C bond dissociation of each C₁₂H₂₆, there are four main types of reactions: H-abstraction, H-addition, intramolecular H transfer, and O-addition. The H-abstraction and O-addition reactions have the highest frequencies. O₂ molecules and H, OH, HO₂, and O radicals also play important roles in promoting the oxidation of C₁₂H₂₆. The first investigation of the early oxidation reaction mechanism of C₁₂H₂₆ provides novel insights into the complex oxidation kinetics of long-chain alkanes.