The scattering and extinction properties of nanodiamonds

Abstract

The study of scattering and extinction properties of possible nanodiamond grains in the ISM are reported. Calculations using Discrete Dipole Approximation (DDA) for varying ellipsoidal shapes and sizes from 2.5 to $10 nm$ are considered. Nanodiamonds show negligible extinction from IR to near-UV and very sharp far-UV rise. Comparison with observations rule out possibility of independent nanodiamond dust but point towards possibility of nanodiamonds as a component in the ISM. Radiation induced transformations may lead to carbonaceous grains with different core and mantles. So calculations are also performed for a core-mantle target model with nanodiamond core in graphite mantles. The graphite extinction features get modified with the peak at 2175 \AA{} being lowered, broadened, blue shifted and accompanied by enhanced extinction in the far-UV. Such variations in the 2175 \AA{} band and simultaneous far-UV rise are observed along some sources. A three component dust model incorporating silicate, graphite and graphite with nanodiamond core is also considered. The model extinction compares very well with the average galactic extinction in the complete range from 0.2 to $10 \mu m^{-1}$. The best fit requires small size and small number of nanodiamonds.Comment: Accepted for publication in MNRAS; 8 Figure

Modelling anomalous extinction using nanodiamonds

“…These sightlines are in general carbon‐rich, having traces of carbonaceous molecules (Roueff et al 2002; Oka et al 2003; Ádámkovics, Blake & McCall 2005); hence the silicate fraction along these sightlines could be lower than the average Galactic abundance. Incorporating other carbonaceous materials supposed to be present in the ISM, namely organic refractory carbon (Li & Greenberg 1997), PAH (Draine & Li 2007), bucky onions (Chhowala et al 2003; Li et al 2008), carbon nanoparticles (Schnaiter et al 1998), nanodiamonds (Van Kerkhoven, Tielens & Waelkens 2002; Binnette et al 2005; Rai & Rastogi 2010), etc., seems more suitable for modelling extinction along these objects.…”

“…a shift towards shorter wavelength that is accompanied by a steep FUV rise. Nanodiamond (ND) extinction shows a steep rise in FUV beyond (Binnette et al 2005; Rai & Rastogi 2010) and considering ND as the core inside a graphite or AMC mantle lowers the bump and shifts the 217.5‐nm peak blueward (Rai & Rastogi 2008, 2010). There is a profile similarity of extinction incorporating NDs inside carbonaceous material with observations along non‐CCM sightlines.…”

“…There is a profile similarity of extinction incorporating NDs inside carbonaceous material with observations along non‐CCM sightlines. Using a ND core inside graphite mantle gives a good match with the average galactic extinction, particularly in the FUV (Rai & Rastogi 2010). Therefore modelling of non‐CCM sites and sites with steep FUV is attempted by incorporating NDs as an additional component, and is being reported.…”

Modeling Dust in the Magellanic Clouds

“…This is also hinted by the numerical tendency during the fitting procedure to go below the lowest limit of 5 nm in particle size, that is systematic for all the lines of sight in the MWG and in the MCs. Such small particles might be carbon mantle fragments, possibly produced during some destructive events (as discussed in the previous paragraph), such as e. g. nanodiamonds (Rai & Rastogi 2010Rai & Botet 2014).…”

Polycyclic Aromatic Hydrocarbons and the Extinction Curve

“…Several works showed that one feasible component with the required properties would be a carbonaceous material in which carbon has an sp 3 structure, such as nanodiamonds or hyperhydrogenated PAHs (see e.g. Rai & Rastogi 2010).…”