Dynamical Behavior of Aromatic Trimer Complexes in Unimolecular Dissociation Reaction at High Temperatures. Case Studies on C₆H₆–C₆F₆–C₆H₆ and C₆H₆ Trimer Complexes

The intramolecular vibrational energy redistribution (IVR) dynamics during unimolecular dissociation of aromatic trimers at high temperatures is the primary interest of this study. Chemical dynamics simulations are performed for the unimolecular dissociation of benzene–hexafluorobenzene–benzene (Bz-HFB-Bz) and benzene trimer (Bz-trimer) complexes at a temperature range of 1000–2000 K. Partial dissociation of both the complexes is observed, which leads to a dimer and a monomer in the dynamics. However, the probability of such dissociation was found much lower in the case of the Bz-trimer, which further decreases with the increase of temperature. The rate of partial dissociation of Bz-HFB-Bz is faster at 1500, 1800, and 2000 K, whereas the rate of complete dissociation of the Bz-trimer is significantly faster than Bz-HFB-Bz at all temperatures. This is just the opposite of the corresponding dimer’s dissociation, where benzene–hexafluorobenzene (Bz-HFB) dissociates at a faster rate than the benzene dimer (Bz-dimer). Thus, the dissociation dynamics of the trimer is different than that of the dimer. Simulations with excited intramolecular and intermolecular modes of the trimer complexes reveal that energy flows from intermolecular to intramolecular modes of Bz-HFB-Bz more freely than the Bz-trimer, and the dissociation process becomes slower for the former. Calculated activation energies for both types of dynamics are much lower than the corresponding binding energies, which may be due to the anharmonicity. The Arrhenius equation with an anharmonic correction factor is considered to recalculate the activation energy and pre-exponential factor

Construction of Diabatic Hamiltonian Matrix from ab Initio Calculated Molecular Symmetry Adapted Nonadiabatic Coupling Terms and Nuclear Dynamics for the Excited States of Na₃ Cluster

We present the molecular symmetry (MS) adapted treatment of nonadiabatic coupling terms (NACTs) for the excited electronic states (2²E′ and 1²A₁^′) of Na₃ cluster, where the adiabatic potential energy surfaces (PESs) and the NACTs are calculated at the MRCI level by using an ab initio quantum chemistry package (MOLPRO). The signs of the NACTs at each point of the configuration space (CS) are determined by employing appropriate irreducible representations (IREPs) arising due to MS group, and such terms are incorporated into the adiabatic to diabatic transformation (ADT) equations to obtain the ADT angles. Since those sign corrected NACTs and the corresponding ADT angles demonstrate the validity of curl condition for the existence of three-state (2²E′ and 1²A₁^′) sub-Hilbert space, it becomes possible to construct the continuous, single-valued, symmetric, and smooth 3 × 3 diabatic Hamiltonian matrix. Finally, nuclear dynamics has been carried out on such diabatic surfaces to explore whether our MS-based treatment of diabatization can reproduce the pattern of the experimental spectrum for system <b>B</b> of Na₃ cluster

Post-Transition State Direct Dynamics Simulations on the Ozonolysis of Catechol in an N₂ Bath and Comparison with Gas-Phase Results

Chemical dynamics simulations on the post-transition state dynamics of ozonolysis of catechol are performed in this article using a newly developed QM + MM simulation model. The reaction is performed in a bath of N2 molecules equilibrated at 300 K. Two bath densities, namely, 20 and 324 kg/m3, are considered for the simulation. The excitation temperatures of a catechol–O3 moiety are taken as 800, 1000, and 1500 K for each density. At these new excitation temperatures, the gas-phase results are also computed to compare the results and quantify the effect of surrounding molecules on this reaction. Like the previous findings, five reaction channels are observed in the present investigation, producing CO2, CO, O2, small carboxylic acid (SCA), and H2O. The probabilities of these products are discussed with the role of bath densities. Results from the gas-phase simulation and density of 20 kg/m3 are very similar, whereas results differ significantly at a higher bath density of 324 kg/m3. The rate constants for the unimolecular channel at each temperature and density are also calculated and reported. The QM + MM setup used here can also be used for other chemical reactions, where the solvent effect is important

Oxidized Charcoal-Supported Thiol-Protected Palladium Nanoparticles for Cross Dehydrogenative Coupling of Heteroarenes

This report describes the synthesis of thiol-protected Pd nanoparticles (NPs) (Pd-MUA) (MUA = 11-mercaptoundecanoic acid) supported on oxidized charcoal (OC-Pd-MUA) at room temperature. The Pd-MUA NPs and OC-Pd-MUA nanocomposites (NCs) were characterized with Fourier transform infrared (FTIR) spectroscopy, transmission electron microscopy (TEM), energy-dispersive X-ray spectrometry (EDX), X-ray photoelectron spectroscopy (XPS), and Brunauer–Emmett–Teller (BET) techniques. The size distribution curve revealed that the diameter of the nanoparticles was in the range of ∼8–12 nm, and the surface area of the NCs was found to be 138.449 m2/g. The as-prepared OC-Pd-MUA NCs were used as a catalyst for the cross dehydrogenative coupling (CDC) of two different heteroarenes. Remarkably, the catalyst was found to be very efficient in activating various heteroarenes under mild reaction conditions. Most importantly, no homocoupled or other byproducts were observed during the heterocoupling reactions. Moreover, the catalyst can be potentially used for the homocoupling reaction of various heteroarenes. It is noteworthy that only 0.22 mol % catalyst loading was required to activate a broad substrate scope with large functional group tolerance. Notwithstanding, the efficacy of the catalyst was found to be retained even after six reaction cycles. The reusability and hot filtration tests validated the heterogeneous nature of the catalysis. In addition, the experimental and computational studies collectively suggested that thiophene derivatives react to produce energetically stable products compared with other heteroarenes during the reaction