S.H. Suck Salk

DWBA predicted relative product rotational state distribution for H + D2 → HD + D

Abstract Relative product rotational state distributions for H + D 2 → HD + D are reported based on the DWBA of Suck Salk, and are shown to agree reasonably well with observations. The rotational peak positions are found to have good correlation with computed “semiclassical” angular momentum.

An effective Hamiltonian study of molecular clusters

Earlier we presented only a qualitative description of a semiempirical effective Hamiltonian method which was successfully applied to the molecular clusters of hydrogen‐bonded (H2O)n. Here a comprehensive analysis of this method is introduced by means of its generalization. Unlike the earlier study, emphasis is placed upon the physical properties of small clusters concerning the energy of formation and the entropy of formation, in order to find propensity rules associated with prenucleation process. It is pointed out that the predicted energy of formation of the molecular clusters at 0 K increases with size, showing slow convergence to the bulk value. Qualitative estimations of entropy changes for small clusters are made, in order to examine entropy effects on the stability of the clusters at finite temperatures. In addition, it is found that the first ionization potential rapidly converges to the work function of ice and the dipole moments of the clusters of open structures tend to linearly increase with...

Comparison between approximate (perturbation) and exact (close-coupling) three-dimensional quantal methods in reactive scattering

Presently the validity of DWBA methods has been largely unchecked with respect to exact methods. In the present study, direct comparison between the DWBA and exact close‐coupling calculations is made by examining reactive scattering angular distributions of H+H2 → H2+H for the same range of collision energy as Schatz and Kuppermann chose. We have found from the DWBA study that (1) the structures of angular distributions between these two methods are remarkably similar at most collision energies; (2) the effect of coupling strongly affects the absolute magnitude of cross sections but not the structures of normalized angular distributions; and (3) the DWBA predicted state‐to‐state integrated (total) cross sections σDWBA are much smaller than the exact close‐coupling results σEXACT, due to the dominant effect of coupling which is found to rapidly increase with collision energy EK, observing the relationship of σEXACT∝E2/3K σDWBA. In addition, the cause of agreement between the approximate DWBA and exact clos...

A unimolecular reaction model approach to the study of desorption of carbon monoxide induced by chemical activation

Abstract A simple model based on the unimolecular reaction (RRKM) theory is described and used to calculate the desorption rate constant of carbon monoxide induced by the exoergic reaction between a gaseous oxygen atom and a surface carbon atom on nickel and platinum surfaces. We find that only a small number of neighbouring surface atoms may participate in the activated complex and are mainly responsible for energy quenching in chemically induced desorption. It is predicted that the desorption rate constant k d decreases with increasing number of the neighbouring surface atoms n , exhibiting an approximately linear relationship between log k d and n .

Electronic structure study of hydrogen-bonded water clusters and linear-chain ice crystal using a modified mndo

Abstract A revised version of MNDO is employed particularly for the treatment of hydrogen-bonded water clusters and linear-chain ice. The computed results of the average hydrogen-bond energies and the first ionization energies for large water clusters and ice are found to correlate well with observation. In addition, using the tight-binding crystal orbital method of LCAO, the band structure of the linear-chain ice is reported.

Growth of ultrafine particles by brownian coagulation

Abstract Current atmospheric observations tend to support the view that continental tropospheric aerosols (particularly urban aerosols) show multimodal mass distributions in the size range of 0.01–100 μm. The origin of these aerosols is both natural and anthropogenic. Recently, trimodal sub-μm size distributions from combustion measurements at 0.008, 0.035 and 0.15 μm were also observed. Our interest in the present study is the secondary process of growth of sub-μm size aerosols by the coagulation process alone. Using the ‘ J -space’ (integer-space) distribution method of Salk (Suck) and Brock (1979, J. Aerosol Sci. 10, 58–590), we report an accurate numerical simulation study of the evolution of ultrafine to fine particle size distributions. Comparision with the analytic solution of Scott (1968, J. atmos. Sci. 25, 54–64) was made to test the accuracy of our J -space or integer-space distribution method. Our multimodal sub-μ particle size distribution study encompassed the particle size range of 0.001–0.20 μm. Details of particle growth in each mode and interaction between different modes in the multimodal distribution were qualitatively analyzed.

Three-dimensional quantal study of favored rotational polarization in H+D2→HD+D

Abstract The single-channel perturbation formalism utilizing the expansion of transition amplitudes in terms of the transferred angular momentum j and its projection m is shown to be useful for studying the cause of favored rotational polarizations in atom-diatomic molecular reactive scattering processes.

Electronic Properties of Water Clusters by an Effective Hamiltonian Treatment

A computationally efficient semi-empirical effective Hamiltonian method1–3 for treating molecular clusters was recently developed. This treatment led to reliable intermolecular binding energies and electronic properties for hydrogen-bonded water clusters in agreement with ab initio calculations4, while other semi-empirical theories failed.5

Systematic studies of homogeneous nucleation processes; discovery of propensity rules

The objectives of this work are: the extraction from experimental data of a simple propensity rule relating nucleation rate and temperature, the demonstration that this rule can be explained in terms of both microphysical nucleation theory based on the fundamental properties of the nucleating molecules and classical theory, the interpretation of this result in terms of classical nucleation theory, and the determination of a temperature dependent sticking coefficient from the application of microphysical nucleation theory to experimental data for water.

A comprehensive study of nucleation rates: A molecular cluster model approach

A Statistical mechanical method is discussed to evaluate the formation energies of homogeneous and heterogeneous clusters. Computed results of homogeneous nucleation rates are in good agreement with the nucleation rate measurements of water.Important to note is that there exists a simple linear relationship between In J (J, the nucleation rate) and I/T (T, the absolute temperature) at all saturation ratios, despite the temperature dependency [] of the formation energy and other prefactors in the expression of nucleation rate.