Laboratory measurements of stretching band strengths of deuterated Quenched Carbonaceous Composites (D-QCC)

Abstract

The observed large variation in the abundance of deuterium (D) in the interstellar medium (ISM) suggests that a significant fraction of D may be depleted into polycyclic aromatic hydrocarbons (PAHs). Signatures of deuteration of PAHs are expected to appear most clearly through C-D stretching modes at 4.4--4.7 micron, whose strengths in emission spectra relative to those of C-H stretching modes at 3.3--3.5 micron provide the relative abundance of D to hydrogen (H) in PAHs once we have accurate relative band strengths of both stretching modes. We report experimental results of the band strength of C-D stretching modes relative to C-H. We employ a laboratory analogue of interstellar carbonaceous dust, Quenched Carbonaceous Composite (QCC), and synthesize deuterated QCC (D-QCC) by replacing the starting gas of CH${}_4$ of QCC by mixtures of CH${}_4$ and CD${}_4$ with various ratios. Infrared spectra of D-QCC are taken to estimate the relative band strengths of the stretching modes, while the D/H ratios in the D-QCC samples are measured with a nano-scale secondary ion mass spectrometer (NanoSIMS). We obtain that the relative strength of aromatic and aliphatic C-D to C-H stretches is 0.56 +/- 0.04 and 0.38 +/- 0.01 per D/H, respectively. The ratio for the aromatic stretches is in good agreement with the results of theoretical calculations, while that of aliphatic stretches is smaller than that of aromatic. The present results do not significantly change the D/H ratios in the interstellar PAHs previously estimated from observed spectra.

arXiv comment8 pages, 1 table, 3 figures, accepted for the Astrophysical Journal

References in corpus (19)

• One percent determination of the primordial deuterium abundance
• Detection of Two Interstellar Polycyclic Aromatic Hydrocarbons via Spectral Matched Filtering
• What is the Total Deuterium Abundance in the Local Galactic Disk?
• Discovery of benzyne, o-C6H4, in TMC-1 with the QUIJOTE line survey
• The primordial deuterium abundance at z = 2.504 from a high signal-to-noise spectrum of Q1009+2956
• The Carriers of the "Unidentified" Infrared Emission Features: Clues from Polycyclic Aromatic Hydrocarbons with Aliphatic Sidegroups
• Deuterated polycyclic aromatic hydrocarbons: Revisited
• PAH Spectroscopy from 1-5 $\mu$m
• Search for the Infrared Emission Features from Deuterated Interstellar Polycyclic Aromatic Hydrocarbons
• Low-Resolution Spectrum of the Diffuse Galactic Light and 3.3 um PAH emission with AKARI InfraRed Camera
• The C--H Stretching Features at 3.2--3.5 Micrometer of Polycyclic Aromatic Hydrocarbons with Aliphatic Sidegroups
• The Deuterium Abundance in the Local Interstellar Medium
• DFT study on interstellar PAH molecules with aliphatic side groups
• Theoretical study of deuteronated PAHs as carriers for IR emission features in the ISM
• Photolysis-induced scrambling of PAHs as a mechanism for deuterium storage
• 13C isotope effects on infrared bands of quenched carbonaceous composite (QCC)
• Deuterated Polycyclic Aromatic Hydrocarbons in the Interstellar Medium: The C--D Band Strengths of Mono-Deuterated Species
• Mid-infrared vibrational study of deuterium-containing PAH variants
• Deuterated Polycyclic Aromatic Hydrocarbons in the Interstellar Medium: The C--D Band Strengths of Multi-Deuterated Species

Cited by in corpus (2)

• Near-infrared spectroscopy of a massive young stellar object in the direction toward the Galactic Center: XCN and aromatic C-D features
• Detection of Deuterated Hydrocarbon Nanoparticles in the Whirlpool Galaxy, M51