Emission limited electrostatic atomization and the fine structure constant

Quadrupole mass spectrometer measurements of charged Octoil sprays reveal that operation in what is interpreted to be the emission limited regime is accurately represented by Z=exp(epsilon 0/epsilon-r(s)/f), where: Z is the fraction of the emission limited charge level, t, the coupling parameter, and f the inverse fine structure constant (137.04). The coupling parameter, defined as 1/(a(0) root pi n), where a(0) is the first Bohr radius, and n the surface charge density (m(-2)), is a nondimensional measure of intercharge spacing, and a fundamental descriptor of two-dimensional (2D) electron structures. The appearance of the coupling parameter, and the fine structure constant as empirical correlating constants for the data implies that the surface 2D electrons are in a gaseous or liquid state. This is consistent with the view that the emission limit-Rayleigh limit transition reflects a phase change of the 2D surface electron cloud from a gas/liquid to a crystalline state. For Octoil, the data indicate that this transition occurs when spray droplet radii are about 0.9 mu m. This corresponds to emission field strength of 0.13 GV/m. Bimodal droplet size distributions characterized by approximately fixed energy levels of one and two Rydbergs [1 Rydberg (Ry) = 13.6 eV], and noncontinuous charging behavior is observed. In all instances studied,. surface charge energy levels are high, and are conveniently ordered in terms of the Rydberg. (c) 2005 American Vacuum Society.