摘要:

We examine fluctuations in cluster evaporation and growth and express these, using the Nyquist and Kubo relations [1,2], in terms of the resistance to single-cluster motion along the coordinate of cluster size. If successful in future development, the methods introduced here will have application to the abstraction of nucleation rates from computer simulations of individual-cluster evaporation/growth events. ©2000 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1361799

出版商:AIP    

年代:1900

数据来源: AIP

摘要:

Homogeneous nucleation rates of light(H2O)and heavy(D2O)water have been measured under identical conditions. Comparing the nucleation rates forH2OandD2Oat the same respective vapor pressurepvand temperatureTthe rates differ by a factor of 2500. However, the individual data points superimpose, if compared at the same supersaturation, i.e., they are the same within experimental scatter. Onset supersaturationsS0forH2Oat nucleation rates ofJ0=107&hthinsp;cm−3&hthinsp;s−1compared with previous measurements by Viisanen &etal;(Viisanen, Y., Strey, R., and Reiss, H.,J. Chem. Phys.,99, 4680 (1993); Erratum: Viisanen, Y., Strey, R., and Reiss, H.,J. Chem. Phys., (2000)in press) show fair agreement. Predictions by the classical nucleation theory-using the most recent expressions for temperature-dependent vapor pressure, surface tension and density-are compared to the experimental data. While the predictions correctly yield the slope of the experimental nucleation rate curves and for one temperature (forH2OT=240&hthinsp;K) even the correct absolute rate, the temperature dependence is experimentally shown to be weaker. ©2000 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1361800

出版商:AIP    

年代:1900

数据来源: AIP

摘要:

The barrier to the ion-induced nucleation for water and methanol were calculated using a Monte Carlo method. The computer simulation confirms Wilson’s findings in 1899 that anion is a better nucleator to produce water droplets than cation with the same magnitude of charge. The simulation also demonstrates that cation is a better nucleator to produce methanol droplets than anion. Structural and energetic analysis of prenucleation embryos offers a molecular insight into the sign preferences for hydrogen-bonding molecules in ion-induced nucleation. ©2000 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1361801

出版商:AIP    

年代:1900

数据来源: AIP

摘要:

We construct a generalized nucleation potential for binary systems, which includes both the thermodynamic and kinetic effects. We show that the major nucleation flux passes through the saddle point (termed the genuine saddle point) of this generalized nucleation potential, even if it no longer passes through the thermodynamic saddle point. The genuine saddle point concept provides a convenient way to identify systems and conditions for which the ridge crossing phenomenon occurs. Our theory agrees approximately with exact numerical results. ©2000 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1361802

出版商:AIP    

年代:1900

数据来源: AIP

摘要:

We measured the homogeneous nucleation of sulfur hexafluoride using a diffusion cloud chamber under conditions that avoid the possibility of non-diffusive modes of transport within the cloud chamber thus ensuring reliable data from our measurements. We extended the critical supersaturation measurements into the critical region forSF6using helium as background gas. ©2000 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1361803

出版商:AIP    

年代:1900

数据来源: AIP

摘要:

A rate theory that accounts for multimolecular addition or loss of molecules from a cluster is developed for the homogeneous nucleation of a liquid from its metastable vapor. Molecular dynamics simulations of Lennard-Jones argon are used to study the evaporation coefficients of Stillinger type clusters. It is shown that steps involving the gain or loss of 2 or 3 atoms at a time make a significant contribution to the dynamics of cluster growth and that these multimolecular steps obey detailed balance. Studies of the lagtime, which to a first approximation should be related to the nucleation rate, shows thatln(t70)is proportional to1/ln2&hthinsp;(S),as predicted by classical nucleation theory. ©2000 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1361804

出版商:AIP    

年代:1900

数据来源: AIP

摘要:

The roles of fluoroalcohols in enhancing the binary clusters with water as compared to aliphatic alcohols, and in lowering the barrier to homogeneous nucleation have been investigated. The results suggest that fluorocarbons in the gas phase can be used to lower the surface tension of the condensation nuclei in supersaturated vapors, and therefore enhance the rate of homogeneous nucleation. ©2000 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1361805

出版商:AIP    

年代:1900

数据来源: AIP

摘要:

The experimental homogeneous nucleation rate data,Jexp(T,S),for water are compared with a steady state Monte Carlo nucleation rate model,JMC(T,S),in which the small cluster energies of formation are determined from a discrete sum of Monte Carlo generated Helmholtz free energy differences,&dgr;fc(n).This formalism includes the&tgr;&hthinsp;ln(n)term of Fisher, where for the critical water clusters (n*>20molecules) we use&tgr;=2.2.It is shown that the&dgr;fc(n)scale like[Tc/T−1]and that the discrete summation overn=2,3,&ellip;8produces a term that cancels the temperature dependence of the monomer flux factor. The result is a scaled form for the nucleation rate,Jscaled(T,S)=J0&hthinsp;exp[−(16&pgr;/3)[&OHgr;(Tc/T−1)]3/(InS)2,whereJ0=1026&hthinsp;cm−3&hthinsp;s−1and&OHgr;=1.47(close to the value predicted by liquid water bulk surface tension). This form has the same T dependence as the data of Viisanen, Strey and Reiss and gives an improved prediction for the data of Miller, Kassner and Anderson. ©2000 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1361806

出版商:AIP    

年代:1900

数据来源: AIP

摘要:

The homogeneous nucleation of water is investigated in a downward diffusion cloud chamber. Nucleation rates are measured as a function of supersaturation to determine whether homogeneous nucleation of water below −40&hthinsp;°C occurs via vapor to liquid or vapor to solid nucleation. ©2000 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1361807

出版商:AIP    

年代:1900

数据来源: AIP

摘要:

We use a recentnon ad hocmodel of microcluster (MM) proposed by Prof. Howard Reiss and co-authors [1,2] together with a more rigorous theory of the nucleation kinetic equation. It is shown that this model satisfactory predicts at least qualitative features of nucleation and the nucleation rate is insensitive to the connectivity distancedc.©2000 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1361808

出版商:AIP    

年代:1900

数据来源: AIP