Incident positive ions

Two main types of experimental equipment which can be distinguished are (a) the perpendicular type in which in the collision chamber the incident positive ions and the product ions move in paths perpendicular to each other (b) the longitudinal type in which the paths are parallel. 

If charge exchange occurs when the incident positive ion passes the neutral gas molecule with a certain velocity, transfer of translational energy will usually take [place. This transfer of translational energy... 

When ionization occurs, an incident electron collides with an atom, producing a positive ion and second electron. Thus two electrons appear after collision where there was only one initially. 

Positive ions start to capture electrons from the medium when their velocity is comparable to that of an electron in an ls-orbital around itself. On further slowing, at first the captured electron is soon lost, and then another electron is captured. Thus cycles of capture and loss continue until it is energetically impossible to lose the captured electron. If the incident particle is multiply charged, another charge exchange cycle will soon be set up, and so on until the particle is reduced to a neutral atom. 

Visible light or other electromagnetic radiation incident on a solid, liquid, or gas can liberate electric charges. This is called photoelectricity. Ejection of electrons from the surface is usually called photoemission. Electrons or positive ions formed in a gas as the result of such radiation is called photoionization. Such a process, however, cannot charge a particle directly. The charging process in that case is a direct result of subsequent diffusion. 

Adsorbed gases can be desorbed from a surface by electron impact. For an ionization gauge this means that, if there is a layer of adsorbed gas on the anode, these gases are partly desorbed as ions by the impinging electrons. The ions reach the ion collector and lead to a pressure indication that is initially independent of the pressure but rises as the electron current increases. If such a small electron current is used so that the number of electrons incident at the surface is small compared to the number of adsorbed gas particles, every electron will be able to desorb positive ions. If the electron current is then increased, desorption " inaease because more electrons impinge on the surfece. This finally leads to a... 

Secondary electrons, i.e. those that have been ejected from atoms by incident radiation, will cause further ionisations or excitations until their energy is reduced to — kT, when they are said to be thermalised. They may then be captured by positive ions or neutral molecules. Since all ionising radiations then basically give rise to these secondary electrons, it is to be expected that their chemical effects will be essentially similar. 

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