Methanol interstellar

The darkness associated with dense interstellar clouds is caused by dust particles of size =0.1 microns, which are a common ingredient in interstellar and circum-stellar space, taking up perhaps 1% of the mass of interstellar clouds with a fractional number density of 10-12. These particles both scatter and absorb external visible and ultraviolet radiation from stars, protecting molecules in dense clouds from direct photodissociation via external starlight. They are rather less protective in the infrared, and are quite transparent in the microwave.6 The chemical nature of the dust particles is not easy to ascertain compared with the chemical nature of the interstellar gas broad spectral features in the infrared have been interpreted in terms of core-mantle particles, with the cores consisting of two populations, one of silicates and one of carbonaceous, possibly graphitic material. The mantles, which appear to be restricted to dense clouds, are probably a mixture of ices such as water, carbon monoxide, and methanol.7... 

This isomeric form is of interest from an interstellar point of view since the isomer, CH3OH2, is a possible route, via dissociative electron-ion recombination, to the observed methanol.14 A proposed reaction68 leading to this isomer is the radiative association,... 

Fig. 3.12 Model of an agglomerate consisting of many small interstellar dust particles. Each of the rod-shaped particles consists of a silicate nucleus surrounded by yellowish organic material. A further coating consists of ice formed from condensed gases, such as water, ammonia, methanol, carbon dioxide and carbon monoxide. Photograph Gisela Kruger, University of Bremen...

As an example, we shall discuss the interstellar synthesis of a compound which is produced on Earth in millions of tons per year methanol. This simplest alcohol was obtained by Robert Boyle in 1661 from the dry distillation of wood. In the molecular clouds of the universe, it is likely that hydrogenation of CO on the surface of dust particles occurs according to the following scheme (Tielens and Charnley, 1997) ... 

Maser transitions have been observed in many important molecules and have been used to carry out surveys of the entire sky. The 22.235 GHz water maser transition is the strongest transition in the radio universe and represents an interesting candidate for an interstellar broadcast frequency. If extraterrestrial intelligence is trying to communicate with us, the choice of the broadcast frequency is an important one and would be known to all intelligent life. Of course it would have a different label, 22.235 GHz being a distinctly Earthly label, but it is a fundamental transition frequency and is observed everywhere. Other maser transitions include the 6.7 and 12.2 GHz methanol maser, the SiO maser v = 1, J = 7-6, 301.8 GHz, which occurs between levels in the first vibration state of the SiO molecule, and finally the OH maser first discovered in 1963 and buried deep in the 2n3/2 electronic state of the hydroxyl radical near 18 cm. This is actually four transitions at 1612, 1665, 1667 and 1720 MHz, all of which must be seen as a group but not necessarily of the same intensity. 

Because most radicals have an odd number of electrons on an atom, the octet rule cannot be satisfied at that atom. It is no surprise, then, that most radicals are unstable species and are quite reactive. They are most often encountered, like carbocations, as transient intermediates in reactions. However, alkyl radicals tend to have longer lifetimes than carbocations because they are less electron deficient, and therefore more stable. In fact, the lifetime of a radical can be appreciable in an environment where nothing is available with which to react. For example, hydrogen atoms are the principal type of matter in interstellar space. And die methyl radical has a lifetime of about 10 min when frozen in a methanol matrix at 77 K. 

It also has been a law of nature for a long time. The physical laws haven t changed much since the universe began—and physicists have checked. In particular, the fine structure constant in 7-bilhon-year-old hght from 7-bilhon-year-old interstellar methanol is the same as today s constant. This means that yesteryear s methanol forms bonds in the same way as today s methanol. The Earth is less than 5 billion years old, and the chemistry behind the Irving-Wilhams series has been constant throughout time. 

A second method is to initially grow an ice of several monolayers and expose this ice to the atomic beam while recording reflection adsorption infrared spectra (RAIRS). In this way, the reactants and products are probed in-situ at the time and temperature that one is interested in, which is the main advantage of this technique. Quantifying the formed product is relatively simple, provided that the RAIRS is calibrated with an independent method. The main disadvantages are that not all species can be detected in this way and that the sensitivity is less than with the previous technique. Most systems have an additional quadrupole mass spectrometer (QMS) installed. So far this technique has been applied to umavel the formation of the main components of interstellar ices, i.e., water, methanol, carbon dioxide, formaldehyde, and formic acid, mainly through H-atom additions to CO- and/or... 

Green SD, Bolina AS, Chen R, Collings MP, Brown WA, McCoustra MRS (2009) Applying laboratory thermal desorption data in an interstellar context sublimation of methanol thin films. Mon Not Roy Astron Soc 398 357-367... 

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