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Title: Quantitative study of cluster growth in free-jet expansions of CO{sub 2} by Rayleigh and Raman scattering

Abstract

The condensation produced in supersonic expansions of CO{sub 2} is studied quantitatively combining Rayleigh and Raman scattering. The cluster number density n{sub c} and the mean cluster size N are obtained for five expansions with stagnation pressures P{sub 0}=1-5 bars, and temperature T{sub 0}=294 K, along axial and radial directions; n{sub c} and N are determined from the condensation onset up to a terminal size N{sub {infinity}}, verifying the empirical law N{sub {infinity}}{proportional_to}P{sub 0}{sup 2.23}. A maximum growth rate dN/dt{approx_equal}8x10{sup 8} s{sup -1} is estimated for the 5-bar expansion. The Raman spectra show a coexistence of solid and liquidlike phases in the jet, with a progressive transition from the liquid to the solid fraction as the clusters increase their size.

Authors:
; ; ;  [1]
  1. Instituto de Estructura de la Materia, CSIC, Serrano 121, 28006 Madrid (Spain)
Publication Date:
OSTI Identifier:
20786528
Resource Type:
Journal Article
Resource Relation:
Journal Name: Physical Review. A; Journal Volume: 72; Journal Issue: 5; Other Information: DOI: 10.1103/PhysRevA.72.053204; (c) 2005 The American Physical Society; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
74 ATOMIC AND MOLECULAR PHYSICS; CARBON DIOXIDE; DENSITY; EXPANSION; LIQUIDS; MOLECULAR CLUSTERS; RAMAN EFFECT; RAMAN SPECTRA; RAYLEIGH SCATTERING; SOLIDS

Citation Formats

Ramos, A., Fernandez, J. M., Tejeda, G., and Montero, S. Quantitative study of cluster growth in free-jet expansions of CO{sub 2} by Rayleigh and Raman scattering. United States: N. p., 2005. Web. doi:10.1103/PHYSREVA.72.0.
Ramos, A., Fernandez, J. M., Tejeda, G., & Montero, S. Quantitative study of cluster growth in free-jet expansions of CO{sub 2} by Rayleigh and Raman scattering. United States. doi:10.1103/PHYSREVA.72.0.
Ramos, A., Fernandez, J. M., Tejeda, G., and Montero, S. Tue . "Quantitative study of cluster growth in free-jet expansions of CO{sub 2} by Rayleigh and Raman scattering". United States. doi:10.1103/PHYSREVA.72.0.
@article{osti_20786528,
title = {Quantitative study of cluster growth in free-jet expansions of CO{sub 2} by Rayleigh and Raman scattering},
author = {Ramos, A. and Fernandez, J. M. and Tejeda, G. and Montero, S.},
abstractNote = {The condensation produced in supersonic expansions of CO{sub 2} is studied quantitatively combining Rayleigh and Raman scattering. The cluster number density n{sub c} and the mean cluster size N are obtained for five expansions with stagnation pressures P{sub 0}=1-5 bars, and temperature T{sub 0}=294 K, along axial and radial directions; n{sub c} and N are determined from the condensation onset up to a terminal size N{sub {infinity}}, verifying the empirical law N{sub {infinity}}{proportional_to}P{sub 0}{sup 2.23}. A maximum growth rate dN/dt{approx_equal}8x10{sup 8} s{sup -1} is estimated for the 5-bar expansion. The Raman spectra show a coexistence of solid and liquidlike phases in the jet, with a progressive transition from the liquid to the solid fraction as the clusters increase their size.},
doi = {10.1103/PHYSREVA.72.0},
journal = {Physical Review. A},
number = 5,
volume = 72,
place = {United States},
year = {Tue Nov 15 00:00:00 EST 2005},
month = {Tue Nov 15 00:00:00 EST 2005}
}
  • Collisional energy transfer, exchange, and complex formation mechanisms for Ar/sub 2/ dimer depletion in free jet expansions have been investigated using quasiclassical trajectory methods on several different potential-energy surfaces. Computed Ar/sub 2/ dissociation cross sections show that V ..-->.. V energy transfer is an unimportant mechanistic pathway for Ar/sub 2/ dissociation in collisions with CO/sub 2/, N/sub 2/, and CO. An R ..-->.. V energy transfer pathway is found to be important at translational energies of 0.03 eV. However, there is very little difference among the results obtained for CO/sub 2/, N/sub 2/, and CO. At higher translational energies, aroundmore » 0.10 eV, the importance of an R ..-->.. V energy transfer mechanism in Ar/sub 2/ dissociation decreases. The results are found to be insensitive to moderate variations in the pairwise LJ(12,6) potential parameters. Three-body potential terms are shown to be of negligible importance. Rate coefficients for collisional dissociation, exchange, and complex formation have been computed for (CO/sub 2/, Ar/sub 2/) and (N/sub 2/, Ar/sub 2/) systems under conditions that approximate those existing in the experiments reported by Yamashita et al. (J. Chem. Phys. 75, 5355 (1981)). For the CO/sub 2/ system, collisional dissociation is the major mechanistic pathway for Ar/sub 2/ depletion. Exchange plays only a minor role. Complex formation does not occur. For the N/sub 2/ system, collisional dissociation predominates for a rotational temperature equal to 298 K. At lower rotational temperatures, exchange becomes the major process. Complex formation does not occur. Yield ratios computed from a simple pseudo-first-order rate model are found to be in good accord with the experimental data for most systems. The exceptions are (C/sub 2/H/sub 4/, Ar/sub 2/) when the mole fraction of C/sub 2/H/sub 4/ is 0.10 or greater, and the (C/sub 4/H/sub 6/, (CO/sub 2/)/sub 2/) system.« less
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