Some Microwave Transitions for Molecules Conjectured to be Present in Comets and in Interstellar Space
Some microwave transitions are investigated for a number of simple molecules composed of the cosmically abundant elements H, C, N, and 0. The list of molecules is limited to those for which microwave data are readily available. From an distribution of the density in a cometary atmosphere the sizes of the (at microwave frequencies) optically thick disks, S , at heliocentric and geocentric distance of 1 a. u. have been calculated. Two temperatures, of 100 0K and 200 0K, have been assumed for the atmosphere, corresponding approximately to the extremes for the gas evaporating from the icy conglomerate nucleus. The high temperatures reached by some dissociation products have not been considered here. If the abundance of some molecules is at least as high as several percent, then microwave emissions from active, "young" comets are on the border of being observable. The largest radius of the "optically" thick disk is obtained for HCN at 100 0K: Si = 2.9- 106 b km, where b < 1, is the number fraction of HCN molecules in the total gas. Arguments are presented against the formation of formaldehyde on dust particles through synthesis from simpler molecules in interstellar space. The presence of interstellar CN indicates that one can expect to find interstellar CO.
Astronomy and Astrophysics
- Pub Date:
- September 1970