ionization

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun The formation of or separation into ions by heat, electrical discharge, radiation, or chemical reaction.
• noun The state of being ionized.

from The Century Dictionary.

• noun In physical chemistry: The electrolytic dissociation of an electrolyte by solution or by fusion.
• noun The process by which a gas is converted into a conductor of electricity; the state or condition of being ionized. See electron, 2, electron theory.

from the GNU version of the Collaborative International Dictionary of English.

• noun (Elec. Chem.) the process of converting neutral atoms or molecules into ions. The process may occur by dissolving an ionic substance in a dissociating solvent, such as water, or by adding or subtracting an electron to or from an atom or molecule. The latter process occurs, for example, in an electron beam in a mass spectrometer and by interaction of substances with ionizing radiation.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun chemistry, physics any process that leads to the dissociation of a neutral atom or molecule into charged particles ions; the state of being ionized

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun the condition of being dissociated into ions (as by heat or radiation or chemical reaction or electrical discharge)
• noun the process of ionizing; the formation of ions by separating atoms or molecules or radicals or by adding or subtracting electrons from atoms by strong electric fields in a gas