Surface, collisions with

Fig. 14. n-Heptane droplet collision with surface at 200 °C. Experimental images (right) are presented by Chandra and Avedisian (1991). We = 45. The size of the last frame is reduced. 

Ion scattering spectrometry (ISS) is also a technique which is sensitive for all elements with an atomic number greater than 2, and measures the energy change of the bombarding ions, caused by elastic collisions with surface atoms. Like SIMS, it has limited spatial capabilities. 

Jf(t) which we shall use in this chapter. We must mention, however, that somewhat more complicated forms have been introduced in order to consider some special aspects of the problem. Some of the most notable include that used by Bloss and Hone (which has a core level in the solid and two orbitals on the atom), those which take into account the scattering of atoms with large velocity components parallel to the surface and that recently considered by Kawai et in order to suggest a possible new experimental technique for studying energy levels of atoms in collision with surfaces. 

An electronically excited molecule can lose its energy by non-reactive collisions in the gas phase or by deactivating collisions with surfaces, and in laboratory studies both processes are probably of importance ... 

Gas-solid chromatography is based on the fact that molecules migrating down the column experience numerous adsorption-desorption events on the walls of the tube and on the surface of an eventual packing. Let us assume that the surfaces are smooth and homogeneous. The simplest theory [6] suggests that at each collision with surface the molecule is adsorbed for a mean time interval ra obeying... 

Chapter 2 calls some fundamental laws and formulae of physical chemistry that are relevant to the content of the book. It deals with diffusion and reactions in gases, as well as with adsorption upon collisions with surfaces, emphasizing the molecular level. It provides some formulae for estimating molecular properties of uncommon compounds. Formulae describing irreversible diffusional deposition of molecular entities and aerosols from flowing gas on the walls of channels are presented quite extensively. 

In an FT-ICR instrument, fragmentation may be achieved by colliding ions with neutrals (CID) but various other strategies are available, such as collision with surfaces (surface-induced dissociation) or bombardment with ultraviolet or infrared radiation from a laser (ultraviolet photodissociation and multiphoton infrared photodissociation). Dissociation may also be achieved by the absorption of black-body radiation produced by a heated vacuum chamber walls (blackbody infrared dissociation). An advantage of these radiation-induced fragmentation methods is that gas pulses are no longer required. Sustained off-resonance irradiation is the preferred, radiation-based method for FT-ICR MS because it is the simplest to implement and tune. Very low energy and multiple excitation collisional activation techniques are also available. 

Ion-Scattering Spectroscopy (ISS). ISS utilizes low energy (0.1-3 KeV) inert gas ions as the incident beam." A fraction of these ions undergo collisions with surface atoms and are backscattered with some loss of energy. Back-scattering will only occur from atoms at the surface, since ion neutralization occurs for incident ions that penetrate beyond the first layer. 

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