ABSTRACT
Ab initio CCSD(T)-F12/cc-pVTZ-f12//B3LYP/6-311G(d,p) calculations of the C4H5O2 potential energy surface have been combined with Rice-Ramsperger-Kassel-Marcus Master Equation (RRKM-ME) calculations of temperature- and pressure-dependent rate constants and product branching ratios to unravel the mechanism and kinetics of the n-C4H5 + O2 reaction. The results indicate that the reaction is fast, with the total rate constant being in the range of 3.4-5.6 × 10-11 cm3 molecule-1 s-1. The main products include 1-oxo-n-butadienyl + O and acrolein + HCO, with their cumulative yield exceeding 90% at temperatures above 1500 K. Two conformers of 1-oxo-n-butadienyl + O are formed via a simple mechanism of O2 addition to the radical site of n-C4H5 followed by the cleavage of the O-O bond proceeding via a van der Waals C4H5OO complex. Alternatively, the pathways leading to acrolein + HCO involve significant reorganization of the heavy-atom skeleton either via formal migration of one O atom to the opposite end of the molecule or its insertion into the C1-C2 bond. Not counting thermal stabilization of the initial peroxy adducts, which prevails at low temperatures and high pressures, all other products share a minor yield of under 5%. Rate constants for the significant reaction channels have been fitted to modified Arrhenius expressions and are proposed for kinetic modeling of the oxidation of aromatic molecules and 1,3-butadiene. As a secondary reaction, n-C4H5 + O2 can be a source for the formation of acrolein observed experimentally in oxidation of the phenyl radical at low combustion temperatures, whereas another significant (secondary) product of the C6H5 + O2 reaction, furan, could be formed through unimolecular decomposition of 1-oxo-n-butadienyl. Both the n-C4H5 + O2 reaction and unimolecular decomposition of its 1-oxo-n-butadienyl primary product are shown not to be a substantial source of ketene.
ABSTRACT
The rotation of optically trapped particles is used in many applications for the realization of different micromechanical devices, such as micropumps, microrotors, and microgyroscopes, as well as for the investigation of particle interactions. Although for transparent micro-objects in both liquid media and vacuum, the rotation can easily be realized by transfer of the spin angular or orbital angular momentum from the light to the object. In the case of light-absorbing micro-objects in gaseous media, such transfers are insignificant in comparison with the thermal effects arising from the photo- and thermo-phoresis phenomena initiating the movement of trapped particles in a laser beam. Currently, proposed methods using a single focused laser beam, tapered-ring optical traps, or single and multiple bottle beams (BBs) have various limitations-for example, the inability to control the direction of the revolution of trapped particles or the low revolution frequency and small revolution angles. Here we propose a simple method for the realization of the revolution of airborne light-absorbing particles. The method is based on a combination of a circular diaphragm and a rotating cylindrical lens, enabling the generation of linear optical BBs. Our results show the flexibility and reliability of the proposed technique, allowing such laser traps to be used in various optical systems for the manipulation of micro-objects with different dimensions and shapes.
ABSTRACT
Formation of fulvene and benzene through the reaction of cyclopentadienyl (C5H5) with methyl radical (CH3) and consequent dissociation of its primary C6H7 products has been studied using ab initio and theoretical kinetics calculations. The potential energies and geometries of all involved species have been computed at the CCSD(T)-F12/cc-pVTZ-f12//B2PLYPD3/aug-cc-pVDZ level theory. Multichannel/multiwell RRKM-Master Equation calculations have been utilized to produce phenomenological pressure- and temperature-dependent absolute and individual-channel rate constants for various reactions at the C6H8 and C6H7 potential energy surfaces. The kinetic scheme combining the primary and secondary reactions has been used to generate the overall rate constants for the production of fulvene and benzene and their branching ratios. Analyses of the kinetic data revealed that at low pressures (0.01 atm) benzene formation prevails, with branching ratios exceeding 60%, whereas at the highest pressure (100 atm) fulvene formation is prevalent, with the branching ratio of benzene being lower than 40%. At intermediate pressures (1 and 10 atm) the two product channels compete and fulvene formation is preferable at temperatures above 1600 K. The results demonstrate that a five-member ring can be efficiently transformed into an aromatic six-member ring by methylation and corroborate the potentially important role of the methyl radical in the mechanism of PAH growth where CH3 additions alternate with H abstractions and acetylene additions.
