Astronomical observational studies are proposed to determine
 the composition, abundance, distribution, and evolution of organic
 molecules (namely aliphatic hydrocarbons and nitriles) on dust
 grains in the interstellar medium. The ultimate goal is to
 understand the processes involved in the formation of these
 prebiogenic compounds, their chemical evolution, and the
 relationship between the compounds in the diffuse and dense
 interstellar clouds. A significant step toward this goal can be
 achieved by measuring the infrared spectrum in the 4500-500 cm-1
 (2.0-20.0 um) region in astronomical objects which span the
 evolutionary range from diffuse clouds through
 quiescent dense molecular clouds. This proposal will only focus
 a subset of these observations, which will complement ongoing
 ground-based and airborne (Kuiper Airborne Observatory) studies.
 The objective for this proposal is
 to study the diffuse ISM dust with ISO observations over two
 wavelength regions that either cannot be studied from the
 ground at all (4.05 - 4.5 um) or sufficiently well (3.2- 3.4 um).
 The observations proposed target three spectral regions that are
 essential to understanding the distrbution of carbon among
 nitriles and hydrocarbons. The three carbonbearing compounds
 of interest are nitriles (4.35 - 4.45 um), polycyclic aromatic
 hydrocarbons in absorption (3.3 um), and the related C-D
 stretch (4.1 - 4.3 um). Ground based studies of the
 aliphatic hydrocarbon (3.4 um) and isonitrile (4.62um)
 absorption features in diffuse and dense clouds,respectively,
 are currently underway.The portions of the spectrum that we cannot
 look at from the ground may hold important keys to the overall
 distribution of carbon among these several types of organic
 materials.