Absolute Photoabsorption Cross-Sections of Methanol for Terrestrial and Astrophysical Relevance

Emanuele Lange, Ana Isabel Lozano, Nykola C. Jones, Søren Vrønning Hoffmann, Sarvesh Kumar, Małgorzata A. Śmiałek, Denis Duflot, Michael J. Brunger, Paulo Limão-Vieira

Research output: Contribution to journalArticlepeer-review

2 Citations (Scopus)

Abstract

We investigate the methanol absorption spectrum in the range 5.5-10.8 eV to provide accurate and absolute cross-sections values. The main goal of this study is to provide a comprehensive analysis of methanol electronic-state spectroscopy by employing high-resolution vacuum ultraviolet (VUV) photoabsorption measurements together with state-of-the-art quantum chemical calculation methods. The VUV spectrum reveals several new features that are not previously reported in literature, for n > 3 in the transitions (nsσ(a′) (2a″)) (1A′ X1A′) and (nsσ, npσ, npσ′, ndσ (7a′)) (1A′ X1A′), and with particular relevance to vibrational progressions of the CH3 rocking mode, v11′ (a″), mode in the (3pπ(a″) (2a″)) (21A′ X1A′) absorption band at 8.318 eV. The measured absolute photoabsorption cross-sections have subsequently been used to calculate the photolysis lifetime of methanol in the Earth's atmosphere from the ground level up to the limit of the stratosphere (50 km altitude). This shows that solar photolysis plays a negligible role in the removal of methanol from the lower atmosphere compared with competing sink mechanisms. Torsional potential energy scans, as a function of the internal rotation angle for the ground and first Rydberg states, have also been calculated as part of this investigation.

Original languageEnglish
Pages (from-to)8496-8508
Number of pages13
JournalJournal of Physical Chemistry A
Volume124
Issue number41
DOIs
Publication statusPublished - 15 Oct 2020

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