Collisional excitation

Collisional excitation

Collisional excitation is a process in which the translational energy of a collision partner is converted into the internal energy of a reactant species.

Astronomy

In astronomy, collisional excitation gives rise to spectral lines in the spectra of astronomical objects such as planetary nebulae and H II regions.

In these objects, most atoms are ionised by photons from hot stars embedded within the nebular gas, stripping away electrons. The emitted electrons, (called photoelectrons), may collide with atoms or ions within the gas, and excite them. When these excited atoms or ions revert to their ground state, they will emit a photon. The spectral lines formed by these photons are called collisionally excited lines (often abbreviated to CELs).

CELs are only seen in gases at very low densities (typically less than a few thousand particles per cm³). At higher densities, the reverse process of collisional de-excitation suppresses the lines. Even the hardest vacuum produced on earth is still too dense for CELs to be observed. For this reason, when CELs were first observed by William Huggins in the spectrum of the Cat's Eye Nebula, he did not know what they were, and attributed them to a hypothetical new element called Nebulium. However, the lines he observed were later found to be emitted by extremely rarefied oxygen.

CELs are very important in the study of gaseous nebulae, because they can be used to determine the density and temperature of the gas.

Mass spectrometry

Collisional excitation in mass spectrometry is the process where an ion collides with an atom or molecule and leads to an increase in the internal energy of the ion.[1] Molecular ions are accelerated to high kinetic energy and then collide with neutral gas molecules (e.g. helium, nitrogen or argon). In the collision some of the kinetic energy is converted into internal energy which results in fragmentation in a process known as collision-induced dissociation.

References

  1. ^ IUPAC, Compendium of Chemical Terminology, 2nd ed. (the "Gold Book") (1997). Online corrected version:  (2006–) "collisional excitation".

Wikimedia Foundation. 2010.

Игры ⚽ Нужно решить контрольную?

Look at other dictionaries:

  • Coronal radiative losses — In astronomy and in astrophysics, for radiative losses of the solar corona, it is meant the energy flux irradiated from the external atmosphere of the Sun (traditionally divided into chromosphere, transition region and corona), and, in particular …   Wikipedia

  • Megamaser — A megamaser is a type of astrophysical maser, which is a naturally occurring source of stimulated spectral line emission. Megamasers are distinguished from astrophysical masers by their large isotropic luminosity. Megamasers produce roughly 103… …   Wikipedia

  • Interstellar medium — Interstellar redirects here. For other uses, see Interstellar (disambiguation). The distribution of ionized hydrogen (known by astronomers as H II from old spectroscopic terminology) in the parts of the Galactic interstellar medium visible… …   Wikipedia

  • Liste de molecules detectees dans le milieu interstellaire — Liste de molécules détectées dans le milieu interstellaire Cet article est une liste de molécules qui ont été détectée dans le milieu interstellaire, groupées par nombre d atomes constituant. La formule brute de chaque composé est mentionnée,… …   Wikipédia en Français

  • Liste de molécules détectées dans le milieu interstellaire — Cet article est une liste de molécules qui ont été détectées dans le milieu interstellaire, groupées par nombre d atomes constituant. La formule brute de chaque composé est mentionnée, ainsi que toute forme ionisée qui aurait éventuellement été… …   Wikipédia en Français

  • Moléculas detectadas en el medio interestelar — Anexo:Moléculas detectadas en el medio interestelar Saltar a navegación, búsqueda Ésta es una lista de moléculas detectadas en el espacio interestelar, agrupadas según el número de átomos constituyentes. Se reseña también su fórmula química,… …   Wikipedia Español

  • Anexo:Moléculas detectadas en el medio interestelar — Ésta es una lista de moléculas detectadas en el medio interestelar, agrupadas según el número de átomos constituyentes. Se reseña también su fórmula química, junto a las formas ionizadas que se han detectado. Contenido 1 Detección 2 Moléculas 3… …   Wikipedia Español

  • Cat's Eye Nebula — Composite image using optical images from the HST and X ray data from the Chandra X ray Observatory Observation data …   Wikipedia

  • Planetary nebula luminosity function — (PNLF) is a secondary distance indicator used in astronomy. It makes use of the [O III| [O III] λ5007 forbidden line found in all planetary nebula which are members of the old stellar populations (Population… …   Wikipedia

  • luminescence — luminescent, adj. /looh meuh nes euhns/, n. 1. the emission of light not caused by incandescence and occurring at a temperature below that of incandescent bodies. 2. the light produced by such an emission. [1885 90; < L lumin (see LUMEN) +… …   Universalium

Share the article and excerpts

Direct link
Do a right-click on the link above
and select “Copy Link”