The Amount of Interstellar Carbon Locked in Solid Hydrogenated Amorphous Carbon

摘要: Some form of hydrogenated amorphous carbon (HAC) is widely regarded as a likely component dust in the diffuse interstellar medium Galaxy. The most direct observational evidence ∼2950 cm −1 C-H stretch feature seen absorption along heavily attenuated lines sight. We have used measured properties one well-characterized HAC sample, together with well-established correlations between structural, optical, and infrared (IR) characteristics materials general, to estimate amount relative hydrogen that must be bound this particular solid space. solution problem remains uncertain because strong dependence mass-absorption coefficient upon H/C ratio materials. about 80 ppM locked up grains ≃ 0.5. A lower than value would require higher depletions result ∼ 2950 profile inconsistent observations. Substantially ratios, which imply low 20 ppM, lead exhibiting efficient blue-green photoluminescence, not observed. Combined observations gas-phase abundance revised reference abundances refractory elements, implies bulk space HAC. In addition careful analysis IR HAC, we present summary UV/visible optical properties, including complex index refraction, for particularly sample shown an spectrum quantitatively consistent latest medium. Subject headings: dust, extinction — infrared: ISM: bands