Systematic Search for Chemical Reactions in Gas Phase Contributing to Methanol Formation in Interstellar Space

Methanol Negative Ion Fragmentation Probed in Electron Transfer Experiments

In this contribution, we report a novel comprehensive investigation on negative ion formation from electron transfer processes mediated by neutral potassium atom collisions with neutral methanol molecules employing experimental and theoretical methodologies. Methanol collision-induced fragmentation yielding anion formation has been obtained by time-of-flight mass spectrometry in the wide energy range of 19 to 275 eV in the lab frame. The negative ions formed in such a collision process have been assigned to CH₃O^-, OH^-, and O^-, with a strong energy dependence especially at lower collision energies. The most intense fragment anions in the whole energy range investigated have been assigned to OH^- and CH₃O^-. Additionally, the potassium cation energy loss spectrum in the forward scattering direction at 205 eV impact energy has revealed several features, where the two main electronic states accessible during the collision events have vertical electron affinities of -8.26 ± 0.20 and -10.36 ± 0.2 eV. Quantum chemical calculations have been performed for the lowest-lying unoccupied molecular orbitals of methanol in the presence of a potassium atom, lending strong support to the experimental findings.

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

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' ← X̃¹A') and (nsσ, npσ, npσ', ndσ ← (7a')) (¹A' ← X̃¹A'), and with particular relevance to vibrational progressions of the CH₃ rocking mode, v₁₁^'(a″), mode in the (3pπ(a″) ← (2a″)) (2¹A' ← X̃¹A') 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.