D. Kane

Condensation of supersaturated vapors of hydrogen bonding molecules: Ethylene glycol, propylene glycol, trimethylene glycol, and glycerol

The critical supersaturations required for the homogeneous nucleation (rate of 1 drop cm−3 s−1) of ethylene glycol, propylene glycol, trimethylene glycol and glycerol vapors have been measured over wide temperature ranges (e.g., 280–400 K) using an upward thermal diffusion cloud chamber. At lower temperatures the experimental nucleation rates are much higher than the predictions of the classical nucleation theory. Glycerol shows the best agreement between experiment and theory in the temperature range of 340–370 K. An apparent increase in the critical supersaturation of glycerol is observed with increasing carrier gas (helium) pressure and this effect is more pronounced at lower temperatures. The results from corresponding states and scaled nucleation models indicate that the nucleation behavior of glycerol is quite different from other glycols. Glycerol requires higher critical supersaturations compared to the other glycols at the same reduced temperatures. This implies quite small critical clusters for ...

Kinetics of ion-induced nucleation in a vapor-gas mixture.

A general solution for the steady-state ion-induced nucleation kinetics has been derived, considering the differences between ion-induced nucleation and homogeneous nucleation. This solution includes a new effect for nucleation kinetics, the interaction of charged clusters with vapor molecules. Analytical expressions for the ion-induced nucleation rate have been obtained for the limiting cases of high and low thermodynamic barriers. The physical explanation of the so-called sign effect is proposed based on multipole expansion of an electric field of the cluster ion. This theory gives good agreement with experiments and is used to elucidate experimentally observed phenomena.

The effect of carrier gas pressure on vapor phase nucleation experiments using a thermal diffusion cloud chamber

Recent measurements of critical supersaturations for the vapor phase homogeneous nucleation of several substances using a diffusion cloud chamber technique exhibit a dependence on the pressure of the carrier gas used in the experiments. A model of droplet growth and motion in a diffusion cloud chamber, combined with the density and temperature profiles of the chamber is presented to explain the pressure dependent results. The model demonstrates that at higher carrier gas pressures the growth of the droplets is retarded and the optical scattering signal from the particles is reduced. It is concluded that the observed effect may not result from a pressure dependence of the nucleation rate, but from a pressure dependence of the droplet growth and motion.

Ion nucleation as a detector: application of REMPI to generate selected ions in supersaturated vapors

Abstract Resonance enhanced multiphoton ionization (REMPI) of aromatic molecules present in a small concentration within a supersaturated host vapor is demonstrated. The method is applied to the study of ion nucleation in supersaturated vapors of methanol, acetonitrile and nonane induced by the molecular ions of benzene, toluene, and p -xylene. With this method it is now possible to selectively and unambiguously generate specific ions of interest and study their nucleating behavior. Furthermore, the selectivity of REMPI combined with the amplification and detection capabilities of nucleation and growth offer valuable analytical features for the identification of trace components in supersaturated vapors.

Modeling nucleation and droplet growth for ion-induced nucleation experiments in diffusion cloud chambers

Abstract A model of ion-induced nucleation, droplet growth and motion processes in a diffusion cloud chamber is presented. The model predicts the arrival time of the droplets with an accuracy greater than 95%. The model also explains the increase in the time corresponding to the maximum of the nucleation pulse with increasing carrier gas pressure. Using this model it is possible to correlate the arrival time of the droplets with the height (temperature and supersaturation) where the nucleation events take place.

Pressure effects on the charge yield and ion nucleation induced by resonance enhanced multiphoton ionization

Abstract The pressure effects on the charge yield and ion nucleation induced by resonance enhanced multiphoton ionization (REMPI) in a diffusion cloud chamber have been investigated. The ion nucleation spectrum is similar to the charge spectrum produced by the chromophore ion, thus providing further evidence for the identity of the nucleating ions. The measured charge decreases as the carrier gas pressure increases. Models based on collisional quenching of the intermediate state and ion-electron collisional recombination have been used to interpret the observed pressure effects.

Characterization of Nanoscale Particles Produced by Laser Vaporization / Condensation in a Diffusion Cloud Chamber

Nanoscale metal oxide particles have been synthesized by using a novel method which combines laser vaporization of metal targets with controlled condensation in a diffusion cloud chamber. The following oxides have been synthesized: ZnO, SiO 2 , Fe 2 O 3 , Bi 2 O 3 , PdO, NiO, AgO, TeO, Sb 2 O 3 , TiO 2 , ZrO 2 , A1 2 O 3 , CuO, In 2 0 3 , SnO 2 , V 2 O 5 and MgO. With this method, the size of the particles can be conveniently controlled by careful control of the degree of supersaturation which is accomplished by adjusting the temperature gradient, total pressure, and partial pressure of the metal vapor generated by laser vaporization in a diffusion cloud chamber. The microscale structures of the SiO 2 and A1 2 0 3 particles exhibit interesting web-like matrices with a significant volume of vacancies. These materials may have special applications in catalysis and as reinforcing agents for liquid polymers.

Kinetics of ion-induced nucleation and ion mobility of pre-critical clusters

Two limiting regimes of ion induced nucleation kinetics are discussed. Analytical expressions for the nucleation rate are obtained. The influence of the molecular nature of the ion on the nucleation rate is shown. Experimental evidence of the limiting regimes is presented.

A New technique for ion nucleation using resonance ionization within supersaturated vapors

Publisher Summary This chapter describes a new technique that allows the study of ion-induced nucleation by well defined ions. The technique is based on resonant two-photon ionization (R2PI) of a chromophore molecule present in a small concentration in a supersaturated host vapor. With this method, it is possible to selectively and unambiguously generate specific ions of interest and study their nucleating behavior. The new method is demonstrated by studying the ion-induced nucleation of supersaturated methanol and acetonitrile vapors by benzene, toluene, and p-xylene molecular ions. The measurements are carried out in a diffusion cloud chamber. The nucleation rate vs. wavelength exhibits the characteristic resonance peak for the R2PI of the chromophore molecule. A preference for the nucleation on positive ions is observed. The new technique allows the detection of impurity aromatic molecules in supersaturated host vapors. The rate of ion nucleation increases with increase in the concentration of the chromophore impurity in the vapor. The condensation of the supersaturated methanol and acetonitrile vapors shows a detectable preference for nucleation on positive ions.