Issue 8, 2018

Untangling the methane chemistry in interstellar and solar system ices toward ionizing radiation: a combined infrared and reflectron time-of-flight analysis

Abstract

Pure methane (CH4/CD4) ices were exposed to three ionizing radiation sources at 5.5 K under ultrahigh vacuum conditions to compare the complex hydrocarbon spectrum produced across several interstellar environments. These irradiation sources consisted of energetic electrons to simulate secondary electrons formed in the track of galactic cosmic rays (GCRs), Lyman α (10.2 eV; 121.6 nm) photons simulated the internal VUV field in a dense cloud, and broadband (112.7–169.8 nm; 11.0–7.3 eV) photons which mimic the interstellar ultra-violet field. The in situ chemical evolution of the ices was monitored via Fourier transform infrared spectroscopy (FTIR) and during heating via mass spectrometry utilizing a quadrupole mass spectrometer with an electron impact ionization source (EI-QMS) and a reflectron time-of-flight mass spectrometer with a photoionization source (PI-ReTOF-MS). The FTIR analysis detected six small hydrocarbon products from the three different irradiation sources: propane [C3H8(C3D8)], ethane [C2H6(C2D6)], the ethyl radical [C2H5(C2D5)], ethylene [C2H4(C2D4)], acetylene [C2H2(C2D2)], and the methyl radical [CH3(CD3)]. The sensitive PI-ReTOF-MS analysis identified a complex array of products with different products being detected between experiments with general formulae: CnH2n+2 (n = 4–8), CnH2n (n = 3–9), CnH2n−2 (n = 3–9), CnH2n−4 (n = 4–9), and CnH2n−6 (n = 6–7) from electron irradiation and CnH2n+2 (n = 4–8), CnH2n (n = 3–10), CnH2n−2 (n = 3–11), CnH2n−4 (n = 4–11), CnH2n−6 (n = 5–11), and CnH2n−8 (n = 6–11) from broadband photolysis and Lyman α photolysis. These experiments show that even the simplest hydrocarbon can produce important complex hydrocarbons such as C3H4 and C4H6 isomers. Distinct isomers from these groups have been shown to be important reactants in the synthesis of polycyclic aromatic hydrocarbons like indene (C9H8) and naphthalene (C10H8) under interstellar conditions.

Graphical abstract: Untangling the methane chemistry in interstellar and solar system ices toward ionizing radiation: a combined infrared and reflectron time-of-flight analysis

Supplementary files

Article information

Article type
Paper
Submitted
29 Aug. 2017
Accepted
26 Sept. 2017
First published
26 Sept. 2017

Phys. Chem. Chem. Phys., 2018,20, 5435-5468

Untangling the methane chemistry in interstellar and solar system ices toward ionizing radiation: a combined infrared and reflectron time-of-flight analysis

M. J. Abplanalp, B. M. Jones and R. I. Kaiser, Phys. Chem. Chem. Phys., 2018, 20, 5435 DOI: 10.1039/C7CP05882A

To request permission to reproduce material from this article, please go to the Copyright Clearance Center request page.

If you are an author contributing to an RSC publication, you do not need to request permission provided correct acknowledgement is given.

If you are the author of this article, you do not need to request permission to reproduce figures and diagrams provided correct acknowledgement is given. If you want to reproduce the whole article in a third-party publication (excluding your thesis/dissertation for which permission is not required) please go to the Copyright Clearance Center request page.

Read more about how to correctly acknowledge RSC content.

Social activity

Spotlight

Advertisements