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Author Topic: Does The Dust Play A Role In Astrochemistry?  (Read 1479 times)

Offline sunnye

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Does The Dust Play A Role In Astrochemistry?
« on: 16/04/2009 02:16:36 »
The dust has several important chemical roles. Obviously, it may shield molecules from the destructive effects of stellar radiation. It also has more active roles. We have seen that free atoms in collision may simply bounce apart before they can form a chemical bond. By contrast, atoms adsorbed on the surface of a dust grain may be held together until reaction occurs. It is believed that molecular hydrogen is formed in this way (i.e., through heterogeneous catalysis) and is ejected from dust grain surfaces into the gas volume with high speed and in high states of vibration and rotation. Other simple molecules, such as H2O, CH4, and NH3, are also likely to form in this way.

In the denser clumps where the gas is very cold, the dust grains are also at a very low temperature (around 10 degrees above absolute zero). Gasphase molecules colliding with such grains tend to stick to their surfaces, and over a period of time the grains in these regions accumulate mantles of ice: mostly H2O ice, but also ices containing other molecules such as CO, CO2, and CH3OH. Astronomers can detect these ices with spectroscopy. For example, water ice molecules absorb radiation at a wavelength about 3.0 micrometers (11.8 10-5 inches), having to do with the OH vibration in H2O molecules; the molecules do not rotate because they are locked into the ice. In instances in which such ice-coated dust grains lie along a line of sight toward a star that shines in the infrared, this 3.0 micrometer (11.8 10-5 inch) absorption is very commonly seen.

Interstellar solid-state chemistry can occur within these ices. Laboratory experiments have shown that ices of simple species such as H2O, CO, or NH3 can be stimulated by ultraviolet radiation or fast particles (protons, electrons) to form complex molecules, including Please put in proper url with no forum advertisements containing several benzene-type rings. The detection by astronomers of free interstellar benzene (C6H6) in at least one interstellar region suggests that this solid-state chemistry may be the route by which these molecules are made.
« Last Edit: 16/04/2009 07:45:42 by Karen W. »


 

Offline Chemistry4me

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Re: Does The Dust Play A Role In Astrochemistry?
« Reply #1 on: 16/04/2009 02:21:12 »
Why does that link about polycyclic aromatic hydrocarbons (PAHs) bring me to a Thai website?

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Heres a link about polycyclic aromatic hydrocarbons (PAHs)
 

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Re: Does The Dust Play A Role In Astrochemistry?
« Reply #1 on: 16/04/2009 02:21:12 »

 

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