The Journal of Physical Chemistry A最新文献

The unnatural nucleic acid base (uNAB), 6-amino-3-methyl-5-nitropyridin-2(1H)one, often referred to as Z can form a base pair with the uNAB 2-aminoimidazo[1,2-a]-1,3,5-triazin-4(8H)-one (referred to as P) and is analogous to a guanine-cytosine (G-C) pair. However, it is well-known that the nonradiative decay pathway of the P-Z pair is significantly different from that of the G-C pair (Cui et al., Front. Chem. 2020, 8, 605117-605125). In this work, we study the excited state processes in Z using state-of-the-art multireference methods and dynamical techniques to ascertain the predominant nonradiative channels. We find that unlike in the natural NABs, the excited state processes in Z are driven primarily by the -NO₂ group rotation. The electron-withdrawing effect of the -NO₂ substituent plays a crucial role. We further ascertained that ultrafast deactivation channels are possible in Z and identified the stationary point geometries that are responsible for these channels.

Measuring absorption spectra of strongly absorbing solutions is usually only possible by diluting the solution. However, the absorption spectra can be heavily influenced by concentration-dependent interactions, so dilution leads to misleading results. To enable reliable absorption measurements of concentrated solutions, we introduce in this work thinning fluid film spectroscopy (TFFS), a simple and highly automatable method. We present three exemplary measurement modes of TFFS suitable for many different applications and validate the TFFS measurements with control data obtained in specialized, low optical path length cuvettes. Additionally, we compare the suitability of the different measurement modes over a broad concentration range and demonstrate the automation possibilities with a spectroscopy robot. Beyond this automated approach for highly efficient and high-throughput lab work, we also show the possibility of direct integration into production systems with an in-line setup, which can be incorporated into a variety of pipe systems. The TFFS method is not limited to samples from material science but can be transferred to a broad variety of research and industry fields, including proteins, food, and pharmaceuticals or also agriculture and forensics.

A high-precision global potential energy surface (PES) is constructed for the Na₃ system based on high-level ab initio calculations and the fundamental invariant neural network (FI-NN) method. The root-mean-square error (RMSE) of the PES is 2.88 cm^-1. The state-resolved quantum dynamics of the ground-state Na + Na₂ (v = 0, j = 0) → Na₂ (v', j') + Na reaction is studied using the time-dependent wave packet (TDWP) method on the new PES. Analysis of the relevant integral cross sections revealed a complicated energy-transfer mechanism during collisions. Similarly, the characteristics of the differential cross sections indicate that the complex-forming mechanism plays a dominant role in the reaction, providing conditions for a comprehensive exploration of the lifetimes of the complexes. Based on the Rice-Ramsperger-Kassel-Marcus (RRKM) theory, the calculated lifetime of the Na₃ complex is approximately 3.9 ns.

This work reports an implementation of a novel realization of the multireference coupled cluster theory formulated in Fock space. Extending the previous formulation carried out in the (1,1) [M. Musial, R. J. Bartlett, J. Chem. Phys. 129, 044101 (2008)], (0,2) [M. Musial, R. J. Bartlett, J. Chem. Phys. 135, 044121 (2011)], and (2,0) [M. Musial, J. Chem. Phys. 136, 134111 (2012)] sectors to the (3,0) sector, we are able to treat structures with three valence electrons. The (3,0) sector describes systems with three electrons added to the reference, which means that in order to perform correlated calculations for the neutral AB molecule, we have to adopt as the reference a triply ionized structure AB³⁺. A desirable situation occurs when such an ion has a closed-shell structure and also dissociates into closed shell fragments. This feature makes it possible to apply the restricted Hartree-Fock scheme for the whole range of interatomic distances. Examples of molecules of this type are the diatomics formed by the atoms of alkali metals and alkaline earth metals. An analogous structure is also exhibited by alkali metal monocarbides. In the current work, we have calculated the potential energy curves and spectroscopic constants for the LiBe, LiC, and NaC molecules.

Perylene monoimide diesters and the corresponding phenyl-linked bichromophores are strongly fluorescent in dilute solution with minimal triplet population after relaxation of the initial Franck-Condon state. The monomer forms nonemissive face-to-face dimers in solution, wherein illumination leads to formation of a spin-correlated, triplet pair with a yield of ca. 13% and with a time constant of 4 ± 1 ps. The triplet pair, which is localized on the aggregate, cannot separate and decays with a mean lifetime of 80 ± 10 ps. The relaxed S₁ state of the weakly coupled, phenyl-linked bichromophores establishes an equilibrium with an intramolecular charge-transfer state over a hundred picoseconds or so, depending on the solvent and the geometry of the linkage. This equilibrium mixture, being dominated by the relaxed S₁ state, decays on the nanosecond time scale in solution at room temperature without implication of a triplet state. Self-association occurs at higher concentration and, for the para-bridged bichromophore, leads to inefficient triplet formation in tetrahydrofuran at room temperature.

We consider carbon monoxide (CO) confined in the hydrogen-bonded building blocks of sI and sII clathrate hydrates, viz., (5¹², 5¹²6², 5¹²6⁴) cages, within the density functional theory-based calculations. We study their response to the applied electric fields in terms of changes in the geometrical parameters, dipole moment, HOMO-LUMO gap, and vibrational frequency shift. We examine the stability of CO clathrate hydrate building block cages and identify a possible indication of the field-induced release of CO.

Here, we report the results of an IR spectroscopy study on heteroclusters of H₂S and H₂O and several of their isotopomers using mass-selective IR spectroscopy in superfluid helium nanodroplets in the range of 2560-2800 cm^-1. Based on DFT calculations on the B3LYP-D3/6-311++G(d,p) level of theory, we were able to assign the experimentally observed O-D stretching bands to heterodimer and heterotrimer clusters. Since no bands of the S-H-bound conformer HSH···OH₂ could be observed, we were able to determine the O-H-bound conformer HOH···SH₂ to be the global minimum structure. A trapping of the local minima in helium nanodroplets was not observed. This is in line with the weaker hydrogen bond expected for H₂S complexes. In these clusters, the interaction energy is expected to be more dominated by dispersion and less dictated by highly directional electrostatic forces.

The reaction between H and HCF₃ is the primary consumption pathway of HCF₃ in the atmosphere and combustion. In this work, ring polymer molecular dynamics (RPMD) calculations are performed to calculate the rate constants of the reaction on a recently developed accurate potential energy surface. 36, 20, and 8 beads are used to compute the rate constants at 350 K ≤ T < 800 K, 800 K ≤ T ≤ 1000 K, and T > 1000 K, respectively. The obtained RPMD rate constants agree well with the experimental measurements. In addition, a detailed analysis of the free-energy curves and transmission coefficients reveals that the quantum tunneling significantly affects the reaction dynamics, even at high temperatures.

We present a diagrammatic notation to derive the quantum-electrodynamic coupled cluster (QED-CC) equations needed for the description for polaritonic ground and excited states. Our presented notation is a generalization of the existing diagrammatic notation of standard electronic coupled-cluster theory. It is used to derive the QED-CC and QED-EOM-CC equations for the QED-CCSD-1-SD and QED-CCSD-12-SD truncation schemes. Furthermore, we present the diagrams for the CC Λ-equations and reduced density matrices which are needed for the calculation of molecular properties.