Can we Observe Gas Phase Nucleation at the Molecular Level?

We propose and discuss an experiment for the study of neutral gas phase nucleation on a molecular level using propane as the condensable gas. The experiment combines a uniform Laval expansion with soft mass spectrometric detection. The uniform Laval expansion allows nucleation experiments under well-defined conditions while the mass spectrometric detection provides molecular-level information on the molecular aggregates formed. It is discussed how one could observe the onset of nucleation and retrieve the size of the critical nucleus from the mass spectra

Characterization of the gaseous spacecraft environment of Rosetta by ROSINA

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/90700/1/AIAA-2011-3822-983.pd

Observation of propane cluster size distributions during nucleation and growth in a Laval expansion

We report on molecular-level studies of the condensation of propane gas and propane/ethane gas mixtures in the uniform (constant pressure and temperature) postnozzle flow of Laval expansions using soft single-photon ionization by vacuum ultraviolet light and mass spectrometric detection. The whole process, from the nucleation to the growth to molecular aggregates of sizes of several nanometers (∼5 nm), can be monitored at the molecular level with high time-resolution (∼3 μs) for a broad range of pressures and temperatures. For each time, pressure, and temperature, a whole mass spectrum is recorded, which allows one to determine the critical cluster size range for nucleation as well as the kinetics and mechanisms of cluster-size specific growth. The detailed information about the size, composition, and population of individual molecular clusters upon condensation provides unique experimental data for comparison with future molecular-level simulations.ISSN:0021-9606ISSN:1089-769

Can we Observe Gas Phase Nucleation at the Molecular Level?

ISSN:0942-9352ISSN:0044-3336ISSN:2196-715

A pulsed uniform Laval expansion coupled with single photon ionization and mass spectrometric detection for the study of large molecular aggregates

We report on a new instrument that allows for the investigation of weakly-bound molecular aggregates under equilibrium conditions (constant temperature and pressure). The aggregates are formed in a Laval nozzle and probed with time-of-flight mass spectrometry in the uniform postnozzle flow; i.e. in the equilibrium region of the flow. Aggregates over a very broad size range from the monomer to particle sizes of 10–20 nm can be generated and studied with this setup. Soft ionization of the aggregates is performed with single photons from a homemade vacuum ultraviolet laser. The mass spectrometric detection provides molecular-level information on the size and chemical composition of the aggregates. This new instrument is useful for a broad range of cluster studies that require well-defined conditions.ISSN:1463-9084ISSN:1463-907

A velocity map imaging photoelectron spectrometer for the study of ultrafine aerosols with a table-top VUV laser and Na-doping for particle sizing applied to dimethyl ether condensation

We present a new experimental configuration for the study of size-dependent, angle-resolved photoelectron and photoion spectra of weakly bound ultrafine aerosol particles targeted at particle sizes below ∼20 nm. It combines single photon ionization by a tunable, table-top vacuum ultraviolet laser at energies up to 18 eV with velocity map imaging detection and independent size determination of the aerosol particles using the Na-doping method. As an example, the size-dependence of the valence photoelectron spectrum of dimethyl ether clusters and ultrafine aerosols is investigated. Up to a mean particle diameter of ∼3–4 nm, the first ionization energy (value at band maximum) decreases systematically (up to ∼1 eV) and the corresponding band broadens systematically (up to a factor of ∼3) with increasing aggregate size. Plateau values for band positions and bandwidths are reached beyond a diameter of ∼3–4 nm. Experimental evidence for the dominance of the fast intermolecular proton transfer over monomer fragmentation reactions upon ionization is presented via photoion imaging.ISSN:0021-9606ISSN:1089-769