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Journal of Physical Chemistry. A

Jakob Petersen, Eli Pollak
The time it takes a particle to tunnel through the asymmetric Eckart barrier potential is investigated using Gaussian wavepackets, where the barrier serves as a model for the potential along a chemical reaction coordinate. We have previously shown that the, in principle experimentally measurable, tunneling flight time, which determines the time taken by the transmitted particle to traverse the barrier, vanishes for symmetric potentials like the Eckart and square barrier.[Petersen, J.; Pollak, E. Tunneling Flight Time, Chemistry, and Special Relativity...
March 20, 2018: Journal of Physical Chemistry. A
Mrinmoy Mandal, Subhendu Ghosh, Biswajit Maiti
Direct dynamics trajectory surface hopping (DDTSH) method has been employed to study the reaction of C(3P) with ethylene (C2H4). Our trajectory simulations show that at a reagent collision energy of 7.36 kcal/mol, there are two possible product channels: propargyl (H2CCCH) + H and carbene (CH2) + acetylene (HCCH). Estimated branching ratios based on trajectory propagations indicates that propargyl radical formation is the dominant channel contributing (94.1±5.2) % of the overall products formation with (5...
March 20, 2018: Journal of Physical Chemistry. A
Hui Hu, Boyi Zhang, Adam Luxon, Thais Scott, Baoshan Wang, Carol A Parish
The 9,10-didehydroanthracene is an aromatic diradical produced by the Bergman cyclization of a benzannulated 10-membered enediyne. It is a 1,4 diradical, similar to para-benzyne. Here we study the spin state occupancy of the ground state of 9,10-didehydroanthracene by employing multireference methods (MR-CISD and MR-AQCC) with different basis sets (cc-pVDZ and cc-pVTZ) and active space sizes (CAS (2,2) through CAS (8,8)). At the CAS (8,8) MR-AQCC/cc-pVDZ level of theory, we find a two-configurational singlet ground state with an adiabatic EST of 6...
March 20, 2018: Journal of Physical Chemistry. A
So-Yoen Kim, Yang-Jin Cho, Ho-Jin Son, Dae Won Cho, Sang Ook Kang
We report the results of photoinduced electron transfer (PET) in a novel dyad, in which a boron dipyrromethene (BODIPY) dye is covalently linked to o-carborane (o-Cb). In this dyad, BODIPY and o-Cb act as electron donor and acceptor, respectively. PET dynamics were investigated using a femtosecond time-resolved transient absorption spectroscopic method. The free energy dependence of PET in the S1 and S2 states was examined on the basis of Marcus theory. PET in the S1 state occurs in the Marcus normal region...
March 19, 2018: Journal of Physical Chemistry. A
Zoltán Klencsár, Zoltán Köntös
Lignite is a rich source of humic substances such as humic and fulvic acids that are natural chelating agents with multifold applications in fields ranging from agriculture to biomedicine. Associations of heterogeneous molecular components constitute to their complex and still unresolved structure. In this work we utilize X-band electron paramagnetic resonance (EPR) spectroscopy to characterize Fe3+ and Mn2+ complexation sites in fulvic acid (FA) extracted from lignite. EPR signals of FA-Fe3+ and FA-Mn2+ complexes are identified and investigated in detail under various conditions by the means of a newly developed program code and associated analysis method that yields an accurate description of the low-field ( geff ≈ 10-3) range EPR signal by assuming discrete distributions in the axial ( D) and rhombic (λ) zero field splitting (ZFS) parameters associated with Fe3+ complexation sites...
March 19, 2018: Journal of Physical Chemistry. A
Quoc Tri Tran, Sheng-Jie Lu, Li-Juan Zhao, Xi-Ling Xu, Hong-Guang Xu, Van Tan Tran, Jun Li, Wei-Jun Zheng
We measured the photoelectron spectra of diatomic AuSi- and AuGe- and conducted calculations on the structures and electronic properties of AuSi-/0 and AuGe-/0. The calculations at the CASSCF/CASPT2 level confirmed that experimentally observed spectra features of AuSi- and AuGe- can be attributed to the transitions from the 3Σ- anionic ground state to the 2Π (2Π1/2 and 2Π3/2), 4Σ-, 32Σ+, and 42Σ+ electronic states of their neutral counterparts. The electron affinities (EAs) of AuSi and AuGe are determined by the experiments to be 1...
March 19, 2018: Journal of Physical Chemistry. A
Chun-Yu Wang, Shuai Jiang, Yi-Rong Liu, Hui Wen, Zhongquan Wang, Ya-Juan Han, Teng Huang, Wei Huang
Ammonia and amines are important common trace atmospheric species that can enhance new particle formation (NPF) in the Earth's atmosphere. However, the synergistic effect of these two bases involving nucleation is still lacking. We studied the most stable geometric structures and thermodynamics of quaternary (NH3)(CH3NH2)(H2SO4)m(H2O)n (m = 1-3, n = 0-4) clusters at the PW91PW91/6-311++G(3df,3pd) level of theory for the first time. We find that the proton transfer from H2SO4 molecule to CH3NH2 molecule is easier than to NH3 molecule in the free or hydrated H2SO4-base clusters, and thus leads to the stability...
March 16, 2018: Journal of Physical Chemistry. A
Li-Hui Mou, Qing-Yu Liu, Ting Zhang, Zi-Yu Li, Sheng-Gui He
Dinitrogen activation/fixation is one of the most important and challenging subjects in synthetic as well as theoretical chemistry. In this study, the adsorption reactions of N2 onto TaCn - ( n = 1-4) cluster anions have been investigated by means of mass spectrometry in conjunction with density functional theory calculations. Following the experimental results that only TaC4 - was observed to adsorb N2 , theoretical calculations predicted that TaC4 - reaction system (TaC4 - + N2 → TaC4 N2 - ) has a negligible barrier on the approach of N2 molecule while insurmountable barriers are located on the reaction pathways of TaC1-3 - /N2 reaction systems...
March 16, 2018: Journal of Physical Chemistry. A
Wesley D Allen
The overarching analytic integrated rate equation for the chemical kinetics of any reversible or irreversible reaction involving an arbitrary number of species and any integral orders is shown to be [EQN1], where ξ(t) is the extent of reaction variable, the fi are roots of a polynomial of order r, the exponents are determined by [EQN2] , and F0 is a factor involving the stoichiometric coefficients and rate constants (k± ). All integrated rate equations of elementary reactions appearing in chemical kinetics are special cases of this universal solution...
March 16, 2018: Journal of Physical Chemistry. A
Stéphanie Essafi, Jeremy N Harvey
For condensed-phase reactions, commonly used kinetic models assume that energy exchange from and to solvent molecules is much faster than any reactive steps. However, it is becoming increasingly evident that this does not always hold true. In this work, we use molecular dynamics simulations to explore the timescale for energy transfer between solvent and solute in some typical organic solvents. As a reference, energy transfer between solvent molecules is also considered. The timescale is found to depend most strongly on the identity of the solvent...
March 16, 2018: Journal of Physical Chemistry. A
Tibor Gyori, Balazs Olasz, Gabor Paragi, Gabor Czako
Accuracy of the different levels of electronic structure theory is frequently studied for stationary-point properties, however, little is known about the effects of the electronic structure methods and basis sets on the dynamics of chemical reactions. Here we report such an investigation for the F- + CH3 I SN 2 and proton-transfer reactions by developing 20 different analytical potential energy surfaces (PESs) obtained at the HF/DZ, HF/TZ, HF-D3(BJ)/DZ, HF-D3(BJ)/TZ, MP2/DZ, MP2/TZ, MP2-F12/DZ, MP2-F12/TZ, CCSD/DZ, CCSD-F12b/DZ, CCSD(T)/DZ, CCSD(T)-F12b/DZ, OQVCCD(T)/DZ, B97-1/TZ, PBE0/TZ, PBE0-D3(BJ)/TZ, M06-2X/TZ, M06-2X-D3(0)/TZ, B2PLYP/TZ, and B2PLYP-D3(BJ)/TZ levels of theory, where DZ and TZ denote the aug-cc-pVDZ and aug-cc-pVTZ basis sets with a relativistic effective core potential and the corresponding bases for iodine...
March 16, 2018: Journal of Physical Chemistry. A
Ruili Shi, Pengju Wang, Lingli Tang, Xiaoming Huang, Yonggang Chen, Yan Su, Jijun Zhao
Using a genetic algorithm incorporated in density functional theory, we explore the ground state structures of fluoride anion-water clusters F-(H2O)n with n = 1-10. The F-(H2O)n clusters prefer structures in which the F- anion remains at the surface of the structure and coordinates with four water molecules, as the F-(H2O)n clusters have strong F--H2O interactions as well as strong hydrogen bonds between H2O molecules. The strong interaction between the F- anion and adjacent H2O molecule leads to a longer O-H distance in the adjacent molecule than in an individual water molecule...
March 16, 2018: Journal of Physical Chemistry. A
Rumpa Pal, Madhusudana Reddy, Bhimareddy Dinesh, Manjunath A Venkatesha, Simon Grabowsky, Christian Jelsch, Tayur N Guru Row
A comparative study of syn vs. anti carboxylic acids in hybrid peptides based on experimental electron density studies and theoretical calculations shows that, in the anti form, all the three bond angles surrounding Ccarboxyl of the -COOH group are close to ~120°, as expected for a C-sp2 atom, whereas in the syn form, the <C-C(O)-Ohydroxyl angle is significantly smaller by 5-10°. The oxygen atom in the carboxyl group is more electronegative in the anti form, so the polarity of the acidic O-H bond is higher in the anti form compared to the syn form,as observed within the limitations of H atom treatment in X-ray diffraction...
March 15, 2018: Journal of Physical Chemistry. A
Yuly Vesga, Carlos Diaz, Jeanne Crassous, Florencio E Hernandez
Herein, we report on the theoretical-experimental analysis of the two photon absorption and circular dichroism spectra of 1-(2-pyridyl)-4-methoxy-carbo[6]helicene derivative (P6). The primary outcomes of our investigation on this particular helicene derivative with a donor-acceptor motif on one end led to two important conclusions: 1) The lengthening of the π-electron delocalization within the helical core of P6 predominantly increases the contribution of the magnetic transition dipole moment to the TPCD signal; 2) The electric transition quadrupole moment contribution to the TPCD signal is enhanced by the intramolecular charge transfer (ICT) produced by the donor-acceptor combination on one end of the molecule...
March 15, 2018: Journal of Physical Chemistry. A
Ewa Erdmann, Marta Łabuda, Nestor Fabián Aguirre, Sergio Díaz-Tendero, Manuel Alcami
We present a complete exploration of the different fragmentation mechanisms of furan (C4H4O) operating at low and high energies. Three different theoretical approaches are combined to determine the structure of all possible reaction intermediates, many of them not described in previous studies, and a large number of pathways involving three types of fundamental elementary mechanisms: isomerization, fragmentation and H/H2 loss processes, this last one was not yet explored. Our results are compared with the existing experimental and theoretical investigations for furan fragmentation...
March 15, 2018: Journal of Physical Chemistry. A
Alexandre Osmar Ortolan, Ina Oestroem, Giovanni Finoto Caramori, Renato Luis Tame Parreira, Eder Henrique da Silva, F Matthias Bickelhaupt
We have explored and analysed the physical factors through which non-covalent in- teractions in anion sensing based on calixarene-type hosts can be tuned, using dispersion- corrected DFT and Kohn-Sham molecular orbital (KS-MO) theory in conjunction with a canonical energy decomposition analysis (EDA). We find that the host-guest interac- tion can be enhanced through the introduction of strongly electron-withdrawing groups at particular positions of the arene and triazine units in the host molecule as well as by coordination of a metal complex to the arene and triazine rings...
March 15, 2018: Journal of Physical Chemistry. A
Melissa P Woodard, Scott T Akin, Collin J Dibble, Michael A Duncan
Ultra-small chromium oxide nanoclusters produced by laser vaporization in a fast flowtube reactor are ligand-coated by gas phase reactions with acetonitrile vapor and then captured in a cold trap and transferred to solution. The resulting clusters are characterized with mass spectrometry, UV-visible absorption and emission, infrared spectroscopy, and surface-enhanced Raman spectroscopy (SERS). According to mass spectrometry, clusters of the form CrxOy(MeCN)z are produced in the size range of x  10 and y < 25...
March 15, 2018: Journal of Physical Chemistry. A
Tingting Wang, Jun Ma, Baoqi Yin, Xiaopeng Xing
We systematically studied the adsorption of O2 on Aun- in the size range of 0-1 nm at low temperatures, and determined new active sizes with n = 22, 24, 34, and 36. The kinetic measurements more clearly showed the correlation between the reactivity of Aun- with O2 and their electronic properties: the sizes with a close electron shell are always inert, and the sizes with a unpaired electron can chemically adsorb one O2 molecule if their adiabatic detachment energies (ADEs) are lower than a threshold around 3...
March 15, 2018: Journal of Physical Chemistry. A
Joshua H Marks, Timothy B Ward, Michael A Duncan
Manganese oxide cluster cations are produced by laser vaporization in a pulsed nozzle source, and detected with time-of-flight mass spectrometry. The mass spectrum contains intense peaks for stoichiometries corresponding to (MnO)n+. Multiphoton photodissociation of these clusters yields smaller ions with the same stoichiometric ratio, either by sequential elimination of MnO units or by various fission processes with roughly equal efficiencies. Fragmentation of clusters containing excess oxygen also yields (MnO)n+ fragments...
March 14, 2018: Journal of Physical Chemistry. A
M Merced Montero-Campillo, Ibon Alkorta, José Elguero
A set of complexes L2HB···BeX2 (L = CNH, CO, CS, N2, NH3, NCCH3, PH3, PF3, PMe3, OH2; X = H, F) containing a boron-beryllium bond is described at the M06-2X/6-311+G(3df,2pd)//M062-2X/6-31+G(d) level of theory. In this quite unusual bond, boron acts as a Lewis base and beryllium as a Lewis acid, reaching binding energies up to -283.3 kJ/mol ((H2O)2HB···BeF2). The stabilization of these complexes is possible thanks to the -donor role of the L ligands in the L2HB···BeX2 structures and the powerful acceptor nature of beryllium...
March 14, 2018: Journal of Physical Chemistry. A
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