An Etymological Dictionary of Astronomy and Astrophysics
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فرهنگ ریشه شناختی اخترشناسی-اخترفیزیک

M. Heydari-Malayeri    -    Paris Observatory

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Number of Results: 5 Search : dissociation
dissociation
  واهزش   
vâhazeš

Fr.: dissociation   

General: An act or instance of dissociating; the state of being dissociated.
Chemistry: Separation of a molecule into two or more fragments (atoms, ions, radicals) by the absorption of electromagnetic radiation or the action of collisional phenomena.

From → dis- + (as)sociation, → association.

dissociation energy
  کاروژ ِ واهزش   
kâruž-e vâhazeš

Fr.: énergie de dissociation   

Energy required to dissociate a molecule. → dissociate.

dissociation; → energy.

photodissociation
  شید-واهزش، نور-واهزش   
šid-vâhazeš, nur-vâhazeš

Fr.: photodissociation   

The → dissociation of a → chemical compound by → radiation  → energy.

Verbal noun of → photodissociate; → -tion.

photodissociation region (PDR)
  ناحیه‌ی ِ شید-واهزش، ~ نور-واهزش   
nâhiye-ye šid-vâhazeš, ~ nur-vâhazeš

Fr.: région de photodissociation   

A neutral region at the boundary of a → molecular cloud created by the penetration of → far ultraviolet (FUV) radiation from associated stars. The FUV radiation (6 eV ≤ hν ≤ 13.6 eV) dissociates the molecules and heats the gas and dust. A warm, atomic → H I region is thus created and the chemistry and thermal balance of the region are determined by the penetrating FUV photons. The progressive absorption of FUV photons leads to the occurrence of transitions between atomic and molecular phases, such as H I/H2 and C II/C I/CO transitions. By extension, any neutral region where the physics is controlled by FUV photons can be called a PDR, as it is the case for → diffuse interstellar clouds or the edge of → circumstellar disks. The PDR concept was first studied by A. G. G. M. Tielens and D. Hollenbach (1985, ApJ 291, 722).

photodissociation + → region.

X-ray Dissociation Region (XDR)
  ناحیه‌ی ِ واهزش ِ پرتوهای ِ ایکس   
nâhiye-ye vâhazeš-e partowhâ-ye X

Fr.: région de dissociation par rayons X   

A region of → molecular clouds whose chemistry is affected by → X-rays from neighboring sources.

X-ray; → dissociation; → region.