Trap Seeker and Digger: The Dual Identity of the Solvated Electron in Methanol

The structure of the solvated electron in methanol is less studied but more complicated than the one of the hydrated electron. In this condensed-phase first principles molecular dynamics study we reveal the nature of the recently discovered shallow and deep trap states of the excess electron and suggest a more complex picture including four bound cavity states classified by the number of the hydroxy-groups coordinated to the electron, their binding energy gradually increasing with the OH-coordination. The initial shallow bound states are formed via a transient diffusion mechanism, in a trap-seeking fashion, whereas, deeper bound states are formed via a slower methanol molecules reorientation. Despite apparent similarity of the absorption spectrum of the solvated electron in methanol to that in water, the origin of the absorption maximum is drastically different. The previously assumed model of hydrogenic transitions (s-p etc.) as is the case in water does not hold for methanol. Instead, the main bands arise due to the charge-transfer states, promoting the excess electron to the nearby cavity, naturally abundant in this solvent. We propose an alternative simple model to describe electronic states of the solvated electron in methanol: the double square well.