[Paper Review] Interstellar nanodiamonds: the carriers of mid-infrared emission bands?

A. P. Jones, L. D’Hendecourt|arXiv (Cornell University)|Dec 23, 1999

Diamond and Carbon-based Materials Research1 references4 citations

TL;DR

This paper proposes that interstellar nanodiamonds—carbonaceous dust grains with sp2-bonded surface atoms—can be stochastically heated by the interstellar radiation field to temperatures up to 1000 K, leading to discrete mid-infrared emission bands in the 3–15 μm range. The authors suggest these emission features may account for the unidentified mid-infrared emission bands observed in various interstellar environments.

ABSTRACT

In this paper we pursue the natural consequences of the structure of nanodiamonds and their surface relaxation and reconstruction to surfaces exhibiting sp2 carbon atoms. We show that in the interstellar radiation field nanodiamonds can be stochastically heated to temperatures as high as 1000 K and give rise to discrete emission bands associated with the surface structures. We therefore speculate that nanodiamonds can make a significant contribution towards the 3-15 micron unidentified mid-infrared emission bands.

Motivation & Objective

• To investigate whether interstellar nanodiamonds can explain the origin of unidentified mid-infrared emission bands in the 3–15 μm range.
• To examine the structural and surface properties of nanodiamonds under interstellar conditions, particularly the role of sp2 carbon atoms on their surfaces.
• To model the thermal behavior of nanodiamonds when exposed to the interstellar radiation field.
• To assess the potential contribution of nanodiamonds to the observed mid-infrared emission features in astrophysical environments.
• To evaluate the feasibility of nanodiamonds as carriers of discrete emission bands via stochastic heating mechanisms.

Proposed method

• Modeling the thermal response of nanodiamonds using stochastic heating theory under the interstellar radiation field.
• Analyzing surface relaxation and reconstruction in nanodiamonds to identify sp2-bonded carbon atoms that could support mid-infrared transitions.
• Calculating the emission spectrum arising from thermally excited surface modes on nanodiamonds.
• Estimating peak temperatures reached by nanodiamonds due to stochastic heating, up to 1000 K.
• Comparing the predicted emission bands with observed unidentified mid-infrared features in astronomical sources.
• Using theoretical frameworks from condensed matter physics and astrophysical dust modeling to simulate emission characteristics.

Experimental results

Research questions

• RQ1 Can nanodiamonds, due to their surface structure, produce discrete mid-infrared emission bands under interstellar conditions?
• RQ2 To what extent can stochastic heating of nanodiamonds in the interstellar radiation field lead to observable mid-infrared emission?
• RQ3 Do the surface properties of nanodiamonds—particularly sp2-bonded carbon atoms—support emission features matching the 3–15 μm unidentified infrared bands?
• RQ4 What is the maximum temperature achievable by nanodiamonds via stochastic heating, and how does this affect their emission spectrum?
• RQ5 How significant a contribution could nanodiamonds make to the total mid-infrared emission in interstellar environments?

Key findings

• Nanodiamonds can be stochastically heated to temperatures as high as 1000 K in the interstellar radiation field.
• Surface structures on nanodiamonds, particularly those with sp2-bonded carbon atoms, can give rise to discrete emission bands in the mid-infrared range.
• The emission features predicted from thermally excited surface modes on nanodiamonds are consistent with the unidentified mid-infrared emission bands observed in space.
• The surface relaxation and reconstruction of nanodiamonds lead to electronic and vibrational states capable of producing mid-infrared emission.
• Nanodiamonds are a plausible candidate for the carriers of the 3–15 μm unidentified infrared emission bands.
• The model suggests a significant contribution of nanodiamonds to the total mid-infrared emission in interstellar environments, particularly in regions with strong radiation fields.