The in-gas-jet laser spectroscopy method relies on the production of uniform and low-temperature gas jets to fully resolve the atomic hyperfine structure and efficiently determine fundamental nuclear properties of short-lived isotopes from, e.g., the hardly accessible actinide and transactinide elements. In this article we present the studies devoted to designing, producing, and characterizing the flow properties of a convergent-divergent (de Laval) hypersonic nozzle with a superior performance for laser spectroscopy applications. A novel flow mapping technique, based on resonance ionization spectroscopy (RIS), has been employed to characterize the local flow properties of an argon gas jet formed by this nozzle, revealing a 61.5-mm long, highly collimated atomic jet at a uniform low temperature of 16.6(5) K [Mach 8.11(12)] that will enable laser spectroscopy experiments on heavy-exotic nuclei with an unprecedented spectral resolution and a high efficiency. These results have been compared with those obtained by planar laser induced fluorescence spectroscopy (PLIFS) studies and show a good agreement between the two techniques and a significant improvement in efficiency of the RIS mapping method with respect to PLIFS. The data are compared to state-of-the-art fluid-dynamics calculations that were carried out to obtain the nozzle contour and simulate its performance, as well as to explain the observation of a possible onset of argon nucleation.@en

We study the process of cluster formation at extreme supersaturations and identify the temperature-supersaturation domain where evaporation can be neglected resulting in a barrierless process with kinetics dominated by the dimer formation. The cluster size distribution obeys the coalescence equation with the pressure-temperature-dependent association rate coefficients ki, j. In view of the crucial role played by kinetics under these extreme conditions, the values of these coefficients calculated within the free molecular collision model are insufficient for the prediction of the nucleation rate and cluster distribution. An alternative is the use of ki, j obtained from the ab initio calculations. We apply these considerations to the analysis of recent water nucleation experiments in the postnozzle flow of a Laval nozzle. Theoretical predictions of nucleation rate are in an excellent agreement with experiment. At the same time, there is a discrepancy in the densities of small clusters. The latter can be attributed to the difference in ki, j extracted from the experimental data and those resulted from the ab initio calculations.@en

The solid–vapor interfacial free energy γsv plays an important role in a number of physical phenomena, such as adsorption, wetting, and adhesion. We propose a closed form expression for the orientation averaged value of this quantity using a statistical mechanical perturbation approach developed in the theory of liquids. Calculations of γsv along the sublimation line for systems characterized by truncated and shifted Lennard-Jones potential are presented. Within the temperature range studied—not far from the triple point—model predictions are in good agreement with molecular dynamics simulations. At the triple point itself the model yields interfacial tensions between the three coexisting phases—solid–vapor, liquid–vapor, and solid–liquid. The latter is obtained by means of Antonow’s rule. All three triple point values perfectly agree with simulation results.@en