Thermal effects in carbonaceous dust.

Details Thermal effects in carbonaceous dust. Thermal effects in carbonaceous dust.

Nov 1996

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1996mnras.283..343d&link_type=abstract

Monthly Notices of the Royal Astronomical Society, Vol. Vol. 283, No. 1, p. 343 - 346

Astronomy and Astrophysics

Astronomy

3

Molecular Processes -- Dust, Extinction -- Ism: Molecules -- Infrared: Ism: Lines And Bands, Interstellar Dust: Molecular Processes, Interstellar Dust: Laboratory Simulations, Interstellar Dust: Thermal Properties, Interstellar Dust: Carbon

Scientific paper

The temperature dependence of optical and IR absorption in hydrogenated amorphous carbon (HAC) shows that the concentration of aromatic (CH) and aliphatic (CHn, where n = 2, 3) groups together with the bandgap energy Eg is a strong function of temperature. The rate constant, k1, describing the closure of the bandgap in HAC, is found to be k1≡ 6.8(s-1) exp[-(8000±2000)/T], and the elimination of H from HAC is also described by k1. At dust temperatures, between 40 and 70 K, CH and CHn concentrations in HAC are enhanced by reaction with H atoms liberated from traps with binding energies 0.05-0.2 eV. I show that the ratio of optical depth for CH (3.3-μm) and CHn (3.4-μm) absorbers, τ(3.3)/τ(3.4), is ⪆1 for dust that has been heated to 50-60 K for an extended time, but is otherwise small in unheated dust. These data also show that partial graphitization of HAC can occur in sources where the dust temperature T ≡ 200 K. The release of partially graphitized 0.001-0.002 μm aromatic clusters in shocks may be the initial stage in the creation of small graphite grains.

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