[Home]Molecular cloud

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Analysing the composition of interstellar clouds is achieved by studying electromagnetic radiation that we receive from them. Large radiotelescopes scan the intensity in the sky for particular frequencies of electromagnetic radiation which are characteristic of certain molecules' spectra. Interstellar clouds are cold and tend to give out EM radiation of large wavelengths. This produces a map of the abundance of these molecules to produce an understanding of the boundaries of clouds.

Different molecules present

Radiotelescopes can also scan over frequencies recording the intensities of each concentrating in on region of space. Peaks of frequencies mean that an abundance of that molecule or atom is present in the cloud. The height of the peak is proportional to the relative percentage that it makes up.

Chemical reactions occuring in these clouds

Evidence for faster reaction rates

The rates of reactions in interstellar clouds were expected to go very slowly with minimal products being produced due to the low temperature and relatively low density (molecules per cubic centimetre) of the clouds. However molecules were observed in the spectra that scientists would not have expected to find at these temperature and pressures, as the reactions needed to create them were thought to not happen in such conditions. However they were found, indicating that the rate of these chemical reactions in interstellar clouds takes place faster than expected from gas
reactions alone. It is believed that reactions in the surface
of grains of dust must play an important role in the chemistry of the clouds.

Simulated data gathering

Further investigation is being pursued by simulating the conditions of interstellar clouds. This is achieved by expanding a mixture of NCNO and a molecular reactant through a nozzle resulting in a supersonic flow of this gas. This is necessary so that the gas is cooled down to an extremely low temperature before it condenses in to solid. This is possible because it takes time for the gas to condense. The NCNO is broken down by a pulsed laser in to CN and NO radicals, of which the CN reacts with the molecular reactant. The rate of reaction is measured by measuring the time it takes for the CN to react, as a laser pulse detects the fluorescence signal which falls after reaction. The rate of reaction was found to be much faster than expected at low temperatures and could pave the way for reactions between organic chemicals.


Molecular clouds are the interstellar clouds that have a density and size enough to permit the formation of H2, molecular hydrogen. However, this molecule is difficult to detect, and the molecule most used to trace the H2 is CO2, carbon dioxide.


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Last edited October 26, 2001 5:31 am by Sodium (diff)