Water nucleation at extreme supersaturation

Abstract

We report water cluster formation in the uniform postnozzle flow of a Laval nozzle at low temperatures of 87.0 and 47.5 K and high supersaturations of lnS ∼ 41 and 104, respectively. Cluster size distributions were measured after soft single-photon ionization at 13.8 eV with mass spectrometry. Critical cluster sizes were determined from cluster size distributions recorded as a function of increasing supersaturation, resulting in critical sizes of 6-15 and 1, respectively. Comparison with previous data for propane and toluene reveals a systematic trend in the nucleation behavior, i.e., a change from a steplike increase to a gradual increase of the maximum cluster size with increasing supersaturation. Experimental nucleation rates of 5 · 1015 cm−3 s−1 and 2 · 1015 cm−3 s−1 for lnS ∼ 41 and 104, respectively, were retrieved from cluster size distributions recorded as a function of nucleation time. These lie 2-3 orders of magnitude below the gas kinetic collision limit assuming unit sticking probability, but they agree very well with a recent prediction by a master equation model based on ab initio transition state theory. The experimental observations are consistent with barrierless growth at 47.5 K, but they hint at a more complex nucleation behavior for the measurement at 87.0 K.

Carbon dioxide and propane nucleation: the emergence of a nucleation barrier

“…The Mach number M and flow temperature T F are determined from p 0 and from the impact pressures p I using the Rayleigh-Pitot equation, which is valid under isentropic flow conditions and for ideal gas behavior (for more information see ref. [24][25][26][27][28][29][30]. Fig.…”

“…The experimental setup has been described in detail in our previous publications, [24][25][26][27][28][29][30] and is thus only briefly discussed here. Fig.…”

“…Therefore, the monomer and the clusters have to be recorded in separate measurements using different experimental settings. 28 A deflector electrode located in front of the MCP is used to deflect the monomer during the cluster measurements to avoid saturation effects on the MCP.…”

“…In this work, we study homogeneous gas phase nucleation of weakly bound CO 2 and C 3 H 8 clusters at the molecular level in the uniform postnozzle flow of Laval expansions using soft single-photon ionization coupled with time-of-flight mass spectrometry. [24][25][26][27][28][29] These experiments provide cluster size distributions as a function of the temperature, the concentration of the condensable gas and the nucleation time. Experimental nucleation rates are directly determined from these timedependent, cluster size-resolved data and compared with predicted nucleation rates.…”

Propane clusters in Titan’s lower atmosphere: insights from a combined theory/laboratory study

“…All these experiments employed the so-called CRESU (French acronym standing for Kinetics of Reactions in Supersonic Uniform Flows) technique to generate continuous cold uniform supersonic flows through de Laval nozzles. Another approach for investigating cluster formation at low temperatures was adopted by Signorell and coworkers, using pulsed cold supersonic flows generated by de Laval nozzles, in which time evolution of propane (Ferreiro et al 2016), toluene (Chakrabarty et al 2017) and water (Lippe et al 2018) cluster distributions were monitored at temperatures ranging from 42 to 56 K for propane, 48 to 77 K for toluene, and at 47 and 87 K for water. In these studies, the evolution of cluster sizes was derived from mass spectrometry ion signals following single photon ionization at 118 nm (13.8 eV).…”