Search results for "Chemical reaction"
showing 10 items of 196 documents
Electrochemical and Spectroelectrochemical Studies of Diphosphorylated Metalloporphyrins. Generation of a Phlorin Anion Product
2015
Two series of diphosphoryl-substituted porphyrins were synthesized and characterized by electrochemistry and spectroelectrochemistry in nonaqueous media containing 0.1 M tetra-n-butylammonium perchlorate (TBAP). The investigated compounds are 5,15-bis(diethoxyphosphoryl)-10,20-diphenylporphyrins (Ph)2(P(O)(OEt)2)2PorM and 5,15-bis(diethoxyphosphoryl)-10,20-di(para-carbomethoxyphenyl)porphyrins (PhCOOMe)2(P(O)(OEt)2)2PorM where M = 2H, Co(II), Ni(II), Cu(II), Zn(II), Cd(II), or Pd(II). The free-base and five metalated porphyrins with nonredox active centers undergo two ring-centered oxidations and two ring-centered reductions, the latter of which is followed by a chemical reaction of the por…
Photochromic System among Boron Hydrides: The Hawthorne Rearrangement
2019
Photoswitchable molecules have attracted wide interest for many applications in chemistry, physics, and materials science. In this work, we revisit the reversible photochemical and thermal rearrangements of the two B20H182– isomers reported by Hawthorne and Pilling in 1966, whose mechanism had not been understood so far. We investigate the rearrangements by means of a joint experimental and computational study with the outcome that B20H182– represents the first boron-based photochromic system ever reported. Both photochemical and thermal isomerizations occur through the same intermediate and involve a diamond–square–diamond (DSD) mechanism. Given the absence within boron chemistry of named …
Anharmonic Vibrational Spectrum and Experimental Matrix Isolation Study of Thioformic Acid Conformers -- Potential Candidates for Molecular Cloud and…
2021
Thioformic acid (TFA) is the sulfur analog of formic acid, the simplest organic acid. It has three analogues HCOSH, HCSOH, and HCSSH, each of them having two rotational isomeric (rotameric) forms: trans and cis where the trans form is energetically more stable. In this article, we study computational energetics and anharmonic vibrational spectrum of TFA including overtone and combination vibrations. We also studied experimental photoisomerization and photodecomposition channels of HCOSH molecules with different wavelengths. We suggest that TFA is a potential sulfur containing candidate molecule for interstellar and planetary observations and discuss these in a light of different radiation e…
Molecular dynamics simulations of elementary chemical processes in liquid water using combined density functional and molecular mechanics potentials.…
1997
A new approach to carry out molecular dynamics simulations of chemical reactions in solution using combined density functional theory/molecular mechanics potentials is presented. We focus our attention on the analysis of reactive trajectories, dynamic solvent effects and transmission coefficient rather than on the evaluation of free energy which is another important topic that will be examined elsewhere. In a previous paper we have described the generalities of this hybrid molecular dynamics method and it has been employed to investigate low energy barrier proton transfer process in water. The study of processes with activation energies larger than a few kT requires the use of specific tech…
The influence of the solvent's mass on the location of the dividing surface for a model Hamiltonian
2019
The Transition State dividing surface is a key concept, not only for the precise calculation of the rate constant of a reaction, but also for the proper prediction of product ratios. The correct location of this surface is defined by the requirement that reactive trajectories do not recross it. In the case of reactions in solution the solvent plays an important role in the location of the dividing surface. In this paper we show with the aid of a model Hamiltonian that the effective mass of the solvent can dramatically change the location of the dividing surface. Keywords: Dynamical systems, Dividing surface, Reactions in solution, 2019 MSC: 00-01, 99-00
Effect of nonequilibrium charge screening in A + B ? 0 bimolecular reactions in condensed matter
1993
The formalism of many-particle densities developed earlier by the present authors is applied to the study of the cooperative effects in the kinetics of bimolecular A +B--*0 reactions between oppositely charged particles (reactants). It is shown that unlike the Debye-Hiickel theory in statistical physics, here charge screening has essentially a nonequilibrium character. For the asymmetric mobility of reactants (DA=0, D~4:0) the joint spatial distribution of similar immobile reactants A reveals at short distances a singular character associated with their aggregation. The relevant reaction rate does not approach a steady state (as it does in the symmetric case, DA=DB), but increases infinitel…
Formation of slow molecules in chemical reactions in crossed molecular beams
2008
T. V. Tscherbul, Ğ Barinovs, J. Klos, and R. V. Krems Department of Chemistry, University of British Columbia, Vancouver, British Columbia, Canada V6T 1Z1 Department of Theoretical Physics, Institute of Chemical Physics, University of Latvia, Riga, Latvia Department of Chemistry and Biochemistry, University of Maryland, College Park, Maryland 20742, USA Received 13 January 2008; revised manuscript received 29 May 2008; published 8 August 2008
Soft X-Ray Irradiation of Methanol Ice: Implication for H2CO Formation in Interstellar Regions
2010
We performed 0.3 keV soft X-ray irradiation of a methanol ice at 8 K under ultra-high vacuum conditions. To the best of our knowledge, this is the first time that soft X-rays are used to study photolysis of ice analogs. Despite the low irradiation dose of 10{sup -6} photons molecule{sup -1}, the formation of formaldehyde has been observed. The results of our experiments suggest that X-rays may be a promising candidate to the formation of complex molecules in regions where UV radiation is severely inhibited.
Two experiments to approach the Boltzmann factor: chemical reaction and viscous flow
2012
In this paper we discuss a pedagogical approach aimed at pointing out the role played by the Boltzmann factor in describing phenomena usually perceived as regulated by different mechanisms of functioning. Experimental results regarding some aspects of a chemical reaction and of the viscous flow of some liquids are analysed and described in terms of macroscopic variables whose temperature dependence is proportional to the Boltzmann factor. A description of a workshop implementing the approach in the framework of an undergraduate course for engineering education and some preliminary results about its pedagogical relevance are then reported.
Self‐similar problems for modeling the surface chemical reactions with the gravitation
1998
The mathematical model of a chemical reaction which takes place on the surface of the uniformly moving vertically imbedded glass fibre material is considered. The effect of gravitation is taken into account. Boussinesq's and boundary layer fittings allow to derive boundary value problems for self‐similar systems of ordinary differential equations. First Published Online: 14 Oct 2010