A large number of elements in certain meteorites have isotopic composition different from that existing in rocks of the earth or the moon. Excess amounts of some isotopes, which are radiogenic daughters, are attributed to the in situ decay of their parent nuclide. Material containing radioactive parents is believed to have been injected into the condensing solar nebula, from astrophysical sites of their production shortly before formation of these grains. Other isotopic anomalies do not show mass dependent pattern which is characteristic of chemical fractionation. They must be primary isotopic abundances, if it is assumed that physico-chemical processes in the solar nebula cannot produce non-mass dependent fractionation. In such a case the observed isotopic ratios characterise elements differently synthesised and injected into the solar nebula which condensed before it had enough time to homogenise. Thus the isotopically anomalous matter has extra solar origin and may contain supernovae condensates, interstellar matter or dust from other stars. The evidence for different isotopic anomalies is briefly summarised and discussed in terms of the current ideas regarding chemical processes occurring in the early solar system.

The level scheme and electromagnetic properties of 148Pm have been studied using 149Sm(d, 3He) and 148Nd(p, nγ) reactions. Combining these measurements with estimates for E2/M1 decay branching ratios leads to the tentative conclusion that 148Pmg,m are in thermal equilibrium during the s-process. The branch at 148Pm then leads to an inferred s-process neutron density of 3 × 108 cm−3.

Though it is now well accepted that some interstellar matter has been preserved in many stone meteorites, the suggestion that iron meteorites also contain pre-solar matter is a recent one. Experimental results will be presented that show that iron meteorites contain isotopically anomalous Xe, Os and Hg. In acid residues of iron meteorites Xe is often depleted in the lightest isotopes, 124Xe and 126Xe. Osmium in many residues is enriched in 184Os. the measured 196Hg/202Hg ratios in some residues of iron meteorites show values 30% of the normal ratio. This pattern is also noted in some portions of a stone meteorite (Ambapur Nagla). These results, while on one hand bring into focus the importance of iron meteorites as preservers of interstellar matter, on the other hand, suggest that the genesis of iron meteorites has been by a non-magmatic process.

Multielemental analysis of chondrules from unequilibrated E3 chondrite Parsa show that the lithophile elements, both refractory and volatile, are enriched and siderophiles are depleted relative to C1 abundances. This behaviour is generally similar to chondrules from unequilibrated ordinary chondrites (UOC). A detailed comparison of compositional trends in chondrules from E3 chondrites (Parsa and Quingzhen) with UOC's indicates that some of the precursor components of chondrules of E3's are different from those of UOC's.

Laboratory investigations of grain mantles are shown to have a direct application to observations of interstellar grains. the experiments have made it possible to show how infrared spectra may be used as a probe not only of the grains as they are but also as they have evolved both chemically and physically. Growth by accretion, ultraviolet photoprocessing, gradual heating, explosions and general effects of grains on interstellar chemistry provide a consistent basis for understanding evolution of grains in terms of interactions with the gas, and ultraviolet radiation in both diffuse and dense regions of space.

A series of experiments in which mixtures of ices are irradiated with ultraviolet light have been performed. the evolution of these simulated interstellar grain mantles is followed by infrared spectroscopy. the appearance of new bands is observed and possible identifications of these bands are discussed.

Grains affect interstellar chemistry in a variety of ways. Most obviously, they extinguish starlight and thus protect molecules in cloud interiors from photodestruction. The grains themselves contain substantial proportions of particular elements which are therefore less readily available for gas phase reactions and for processing into molecules. Grains in dense clouds are known to accrete molecular mantles which may be further processed; the mantle material is ultimately returned to the gas, either near hot stars or when the clouds are dissipated. Molecular hydrogen, the key to all gas phase chemistry, is undoubtedly formed efficiently on grains, and a plausible mechanism can now be identified. Other molecules, too, form preferentially at surfaces. Finally, the destruction of grains via chemical erosion and by sputtering in shocks provides a substantial molecular contribution to the gas in local regions.

Many gases, including CO, should be condensed at the temperature of interstellar grains in the absence of efficient desorption mechanisms. We consider such mechanisms and find that impulsive heating by X rays and heavy cosmic rays (iron group) are the most efficient ones.

For CO rich mantles, we conclude that species as CO, N2, O2 and probably H2CO, NH3, H2O should be desorbed in most cases including dense and obscure regions. for mantles composed mainly of refractory ices (H2CO, NH3, H2O) we expect very little desorption.

The case of PAH molecules that may offer a larger surface for condensation than grains is also discussed.

There is substantial evidence of the presence of polycyclic aromatic molecules, mainly hydrocarbons (PAH's) in the interstellar medium (Léger and Puget, 1984, Allamandola et al. 1985, Léger and d'Hendecourt in these proceedings). They should contain typically NC = 20–100 carbon atoms, and they can contain perhaps 1–10% of the total interstellar carbon. I have recently discussed in detail their physical and chemical properties (Omont, 1986), which should be intermediate between that of conventional interstellar molecules and grains.

The outer envelopes of the outflows from late-type stars where the dust and molecules have already been formed and the matter has been accelerated to its terminal velocity are the focus of this review. One major role for grains in the circumstellar chemistry is the protection of molecules against photodissociation by ambient interstellar ultraviolet photons. Also, in more distant regions where the grains become sufficiently cool as they flow away from the central star, the dust may serve as a condensation sink for molecules which can be bound into mantles.

We have obtained spectra in the three micron region of a sample of IRAS sources showing a strong 11.3 micron emission feature in their IRAS Low-Resolution Spectra (LRS). The observations have been carried out from ESO (La Silla, Chile) and from UKIRT (Mauna Kea, Hawaii), between March and September 1985. All sources but one turn out to have a more or less strong 3.3 micron emission feature, and additionally in most cases a feature at 3.4 micron, extending into a plateau from 3.45 to 3.60 micron. in one particular case we have resolved the plateau into 3 features at 3.45, 3.51 and 3.56 micron. These are detected for the first time.

The nature of the Very Small Grains evidenced by K. Sellgren (1985) is discussed. Their stability suggests that they are graphitic material and specifically Polycyclic Aromatic Hydrocarbons (PAHs). The expected IR emission of a typical PAH, coronene, gives an impressive spectroscopic agreement with the five observed “Unidentified IR Emission Features”, leading to an unambiguous identification. Those PAHs are the most abundant organic molecules detected to this date (f ~ 10−5).

Equilibrium calculation containing 211 species of 22 elements has been used to study the effect of condensation on molecular abundances as a function of temperature (T) and pressure (P). The condensation of 162 species are tested and 65 species in solar composition and 64 in a C-rich composition have been found to condense. The calculations show the expected result that the abundances of molecules containing condensable elements like Si, Al, Mg, Fe, Zr and Ti in solar composition and C together with above elements in carbon rich composition reduce significantly with condensation. Surprisingly, the abundances of molecules containing S, F and Cl in solar composition and O, S, F and Cl in carbon rich composition are enhanced with condensation but abundances of molecules containing CO like H2CO, HCO in carbon rich composition hardly varies.

The chemical composition of the ice and grains in a cometary nucleus is discussed by applying the condensation theory. The equilibrium condensation theory of a gas having the elemental abundances in the solar system is briefly reviewed. The composition of solids predicted by the equilibrium condensation theory is compared with that of the ice and grains in the nucleus; the latter is inferred from the observations of cometary molecules and grains. On the basis of the results of this comparison, a scenario for the formation history of comets is proposed, and discussion is given on the temperature and region of the primordial solar nebula where comets formed.

A brief summary of the content of the papers comprising the symposium is presented.

A general review is given of the astrophysical information obtainable from observations of molecules in stellar photospheres. Through selected examples, the use of molecules as thermometers (e.g., the OH 3 μm V-R lines in the Sun and α Ori) and as probes of the isotopic (e.g., iMg in metal-poor dwarfs, 12C/13C in cool carbon stars) and elemental abundances (e.g., CNO in red giants) is sketched. All of the (carefully) selected analyses assume that local thermodynamic equilibrium (LTE) prevails.