Dissociation dynamics in the 3-body breakups of methanol upon valence photo double ionization

S. Kumar¹, M. Shaikh¹, W. Iskandar¹, R. Thurston¹, M. A. Fareed¹, D. Call², R. Enoki², C. Bagdia³, N. Iwamoto³, T. Severt³, J. B. Williams², I. Ben-Itzhak³, D. S. Slaughter¹, and Th. Weber<sup>1



1</sup>Chemical Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, CA-94720, USA

²Department of Physics, University of Nevada, Reno, NV-89557, USA

³J.R. Macdonald Laboratory, Department of Physics, Kansas State University, Manhattan, NS-66506, USA

We investigated the valence photo double ionization (54eV) of single methanol molecules, which represent the simplest hydrocarbon with a hydroxyl and methyl group, hence can be considered methyl substituted water, using the COLTRIMS (COLd Target Recoil Ion Momentum Spectroscopy) technique. We were able to detect the momenta of two ejected electrons and nascent photo-fragments in coincidence. We focused on two competing 3-body fragmentation channels resulting in

(a) CH₃OD+ hv (54 eV) -> (CH3OD)*²⁺ + 2e^- -> CH₂⁺ + OD⁺ + H + 2e^-

(b) CH₃OD+ hv (54 eV) ->(CH3OD)*²⁺ + 2e^- -> CH₂⁺ + OD + H⁺ + 2e^-



Electron transfer has been reported to contribute to the photodissociation via spin orbit coupling (SOC) [1] , which we recently found to contribute to the photo dissociation of deuterated water molecules. We derived the electronic energy sharing, the electron-ion energy sharing, as well as the fragment pair momentum sharing distributions.

From these observables we concluded that both reactions are initiated on the same manifold of dication states, but that channel (a) is almost solely driven by direct double ionization and results in an instant 3-body breakup. On the other hand, reaction channel (b) shows a contribution from both, direct double ionization and autoionization, which mainly initiates a sequential breakup into with a subsequent electron transfer from the hydroxyl group to the proton.

From Momentum sharing maps it is clearly visible that for reaction (a) H/OD+ are highly correlated and are dominant in comparison to reaction (b)

Investigations of the relative fragment emission angles and recoil frame photoelectron angular distributions as well as a native frame analysis are underway to further track down the role of SOC in the charge transfer process.

References:

[1] W. Iskander et.al. J. Chem. Phys. 159, 094301 (2023).