Raman Spectroscopic Study of Pyrene in Cosmic Dust Analogues: Evolution from the Gas to the Solid Phase

Abstract

Raman spectroscopy was employed to characterize pyrene (C16H10), the smallest peri-condensed polycyclic aromatic hydrocarbon (PAH), in microcrystals and in pyrene-derived nanograins. Laboratory spectra in the 200–2000 cm–1 Raman shift region were obtained with a 532 nm laser. The spectrum of microcrystalline pyrene consists of narrow bands (FWHM ∼7 cm–1), in good agreement with previous laboratory measurements of single and powder pyrene crystals, and was compared to density functional theory-computed Raman scattering activities of gas phase pyrene monomer and pyrene tetramer clusters, showing that packing in crystals induces shifts in band positions to higher wavenumbers. On the other hand, the spectrum of pyrene-derived nanograins exhibits a broad graphitic G band at 1587 cm–1 (FWHM ∼56 cm–1) and multiple disorder D bands, the largest one at 1388 cm–1 (FWHM ∼101 cm–1), attributed to defects in the carbonaceous structure. When compared to the D-to-G band strength ratios from the insoluble organic matter (IOM) found in various carbonaceous chondrites, the values found for the pyrene nanograins match those from the highly disordered Allende meteoritic IOM best.

Pyrene and Biochar (Raman Spectroscopy)

“…Here we illustrate some Raman spectra of Pyrene. We will see that Gavilan et al, 2022, in the case of pyrene generated nanograins, obtained a spectrum which looks like that of biochar. We will also consider the results obtained by Smith et al, 2016, about their proposal of a structural analysis of char made by means of Raman spectroscopy.…”

“…Pyrene is a single, well-defined molecule, made of four fused benzene rings. It is a polycyclic aromatic hydrocarbon (PAH) molecule, which can be obtained by means of various processes, including the incomplete combustion of organic matter (such as wood and tobacco) and the photoionization of larger hydrocarbons, as it happens in the interstellar space (Gavilan et al, 2022). Pyrene photoionization is studied to understand its electronic structure and for the development of new materials (Figueira-Duarte & Mullen, 2011).…”

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Pyrene is a polycyclic aromatic hydrocarbon (PAH) organic compound. Here we consider its Raman spectroscopy, and how it is revealing, when used to create nanograins (Gavilan et al, 2022), a spectrum which is like that we can observe when biochar is investigated. Besides the approach by Gavilan and coworkers, the research by Smith et al, 2016, based on the Raman spectra of several PAH compounds, and proposed to determine an assignment for the bands of char, will be considered too.

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First Optical Constants of Laboratory-generated Organic Refractory Materials (Tholins) Produced in the NASA Ames COSmIC Facility from the Visible to the Near Infrared (0.4–1.6 μm): Application to Titan’s Aerosols

“…The gas phase can be monitored with mass spectrometry (Ricketts et al 2011;Contreras & Salama 2013;Sciamma-O'Brien et al 2014;Raymond et al 2018;Dubois et al 2023) and cavity ring-down spectroscopy (e.g., Biennier et al 2006, Bejaoui & Salama 2019Bejaoui et al 2023). The solid particles can be deposited onto various substrates for ex situ analyses (e.g., Sciamma-O'Brien et al 2017;Gavilan Marin et al 2020, Gavilan et al 2022Sciamma-O'Brien & Salama 2020;Li et al 2022;Nuevo et al 2022).…”

From Protosolar Space to Space Exploration: The Role of Graphene in Space Technology and Economy

“…Simulation experiments have provided evidence of the chemical steps and physical pathways leading to the formation of two-dimensional sp2-carbon nanostructures in deep space. The current hypothesis is that graphenic structural units originated from a protosolar carbon reservoir and were synthesized in a high-temperature zone near the proto-Sun and during the solar system’s earliest era [ 5 , 6 ]. Most likely, these hexagonal honeycomb structures were generated by the shock-induced decomposition of hydrogenated amorphous carbon grains, which should be very abundant in the circumstellar shells of dying stars.…”