Toward size-dependent thermodynamics of nanoparticles from quantum chemical calculations of small atomic clusters: a case study of (BO).

We present a method for obtaining canonical partition functions and, accordingly, temperature-dependent thermodynamics of arbitrary-sized (nano) particles from electronic structure calculations of the corresponding small size atomic clusters. The guiding idea here is to extrapolate the basic properties underlying the thermochemistry of clusters (electronic energies, rotational constants, and vibrational frequencies) rather than the thermodynamic functions themselves. The thus obtained scaling dependences for these basic properties expressed in a simple analytical form provide an efficient tool for fast evaluation of the size-selected thermochemical data for particles of any nuclearity.

Reaction of the N Atom with Electronically Excited O Revisited: A Theoretical Study.

The kinetics of the reaction of N with electronically excited O (singlet aΔ and bΣ states), potentially relevant for NO formation in nonthermal air plasma, is theoretically studied using the multireference second-order perturbation theory. The corresponding thermodynamically and kinetically favored reaction pathways together with possible intersystem crossings are identified. It has been revealed that the energy barrier for the N + O(aΔ) → NO + O reaction is approximately twice the barrier height for the counterpart process with O(Σ).

Molecular Collision Diameters and Electronic Polarizabilities: Inherent Relationship and Fast Evaluation.

The collision diameter σ for a large set of molecular species is related to the static electronic polarizability α. A remarkable correlation between these quantities conceptually similar to the analogous one previously identified for atoms is revealed. Our recommended model is the function σ(α) = + α, where = 0.

Reaction of H with O in Excited Electronic States: Reaction Pathways and Rate Constants.

Comprehensive quantum chemical analysis with the use of the multireference state-averaged complete active space self-consistent field approach was carried out to study the reactions of H with O in aΔ, bΣ, cΣ, and A'Δ electronically excited states. The energetically favorable reaction pathways and possible intersystem crossings have been revealed. The energy barriers were refined employing the extended multiconfiguration quasi-degenerate second-order perturbation theory.

Theoretical Study of the Reactions of Methane and Ethane with Electronically Excited N2(A(3)Σu(+)).

Comprehensive quantum chemical analysis with the usage of density functional theory and post-Hartree-Fock approaches were carried out to study the processes in the N2(A(3)Σu(+)) + CH4 and N2(A(3)Σu(+)) + C2H6 systems. The energetically favorable reaction pathways have been revealed on the basis of the examination of potential energy surfaces. It has been shown that the reactions N2(A(3)Σu(+)) + CH4 and N2(A(3)Σu(+)) + C2H6 occur with very small or even zero activation barriers and, primarily, lead to the formation of N2H + CH3 and N2H + C2H5 products, respectively.

Physics and chemistry of the influence of excited molecules on combustion enhancement.

The paper addresses detailed analysis of kinetic processes in the H(2)-O(2), CO-O(2) and CH(4)-O(2)-reactive systems upon the presence of singlet oxygen molecules O(2)(a(1)Δg) and [Formula: see text] and the influence of the activation of oxygen molecules in electric discharge on the acceleration of ignition in the H(2)-O(2) and CH(4)-O(2) mixtures. The possibility of the intensification of CO oxidation due to excitation of O(2) and N(2) molecule vibrations and generation of singlet oxygen molecules is also considered. It is shown that the effect of accelerating the ignition strongly depends on the reduced electric field and, as a consequence, on the composition of discharge plasma as well as on the features of chain mechanism development in oxy-fuel systems.

Physical and thermodynamic properties of Al(n)C(m) clusters: quantum-chemical study.

Geometrical structures and physical properties, such as rotational constants and characteristic vibrational temperatures, collision diameter, enthalpy of formation, dipole moment, static isotropic polarizability, and magnetic moment of different forms of Al(n)C(m) clusters with n = 0-5, m = 0-5, have been studied with the usage of density functional theory. Different forms of clusters with the electronic energy up to 5 eV have been identified by using the original multistep heuristic algorithm based on semiempirical calculations and density functional theory. Temperature dependencies of thermodynamic properties such as enthalpy, entropy, and specific heat capacity were calculated for both the individual isomers and the Boltzmann ensembles of each class of clusters.