General discussion after session I

Abstract

D. A. Williams ( UMIST, Manchester, U. K. ) . I wish to highlight some of the interesting and possibly controversial points that were raised. Professor Tayler gave us a very good introduction to the subject and I expect we shall discuss the questions that he raised on abundance anomalies and in particular the survival of grains. There are two particular aspects that interest me. First there is deuterium fractionation in the interstellar medium and it is, of course, known that deuterium fractionation occurs in meteorite material. That seems to indicate that material was fractionated in cold conditions and that the conditions have remained cold ever since because, if the temperature gets above ca . 200 K, that fractionation will disappear. The other point that I found particularly interesting in recent literature is the detection of diamond in the carbonaceous component of certain meteorites and again this seems to indicate a low-temperature regime for that particular material; diamond not being the most stable form of carbon. In Professor Kroto’s stimulating talk there were raised a number of questions, but not so much about chemistry of the interstellar medium as on chemistry in the laboratory or possibly chemistry in circumstellar regions; the main question that I would expect to hear discussed today is that of the applicability of what he has done. Very exciting though it is, there is some uncertainty about the applicability of his work to the problems that we are considering in this particular meeting. The conditions that you might find in the circumstellar regions are obviously not going to be quite like the conditions produced in the laboratory. The second important question that I would expect to be addressed in discussion now is the following. As material moves out of the circumstellar regions into the interstellar regions are the structures that Professor Kroto was describing expected to persist or not? He mentioned that C 60 may be formed in Bunsen burners and he also said that C 60 is very stable. If that is so why is all carbon on the earth not in the form of C 60 ? There must be some destruction mechanisms applying to these structures. Actually, if one makes amorphous carbon by having a surface in a carbon rich medium then, in fact, one does not get the sort of structures that he talked about. A mixture of diamond-like and graphitic-like regions of fairly small extent, perhaps a few tens of angstroms, is found.