|
1 Introduction
|
|
|
2 Observations
|
|
|
3 Characteristics of the extragalactic sources
|
|
|
4 3.4  m absorption feature
|
|
|
5 The 3.4 m hydrocarbons/10 m silicates ratio
|
|
|
6 Galactic center and extragalactic mid infrared spectra
|
|
|
7 Constraints on the nature of the hydrocarbons
|
|
|
8 Conclusions
|
|
|
Appendix: Integrated absorbances of ketones and alcanes at 10 K
|
|
|
References
|
