The traditional view of dust in the interstellar medium is that it is made of graphite and silicates. In this paper, we discuss the evidence for complex organics being a major component of interstellar dust. Comparison between astronomical infrared spectra and laboratory spectra of amorphous carbonaceous materials suggests that organics of mixed aromatic-aliphatic structures are widely present in circumstellar, interstellar, and galactic environments. Scenarios for the synthesis of these compounds in the late stages of stellar evolution are presented.

ABSTRACT
1. INTRODUCTION
2. THE PAH HYPOTHESIS
3. THE MAON HYPOTHESIS
4. PATHWAY OF ORGANIC SYNTHESIS
5. TIME SCALE OF CIRCUMSTELLAR SYNTHESIS
6. RELATIONS WITH OTHER UNEXPLAINED SPEC-TRAL PHENOMENA
7. CONCLUSIONS
REFERENCES

• Sun Kwok(Space Astronomy Laboratory, Faculty of Science, The University of Hong Kong)