Equilibrium structure, fluctuations, and spectroscopy of a solvated electron in methanol

Structural and spectroscopic properties of the equilibrium excess electron solvated in methanol are evaluated via adiabatic quantum molecular dynamics simulations employing an electron-methanol pseudopotential based on that of Zhu and Cukier et al. [J. Chem. Phys. 98, 5679 (1993)]. The solvated electron is localized in a roughly spherical ground electronic state of 2.5 Å radius. The electron is surrounded by approximately six or seven methanol molecules in the first solvent shell with mostly O–H bond orientation. Due to the strong electron-methanol coupling, solvent fluctuations result in substantial fluctuations of energy, size, and shape of the electron. The influences of radial fluctuations and asymmetric distortions of solvent cavities are illustrated on both the solvation structure and the optical spectrum. The optical-absorption spectrum of the solvated electron is dominated by transitions to three clearly nondegenerate $p$ -like excited states. The fluctuations influence the $\mathrm{s-p}$ energy gap and modulate the $\mathrm{p-p}$ energy splitting leading to the calculated broad, featureless optical band. Comparison between systems containing flexible and rigid methanol molecules is also reported. Unlike in water, characteristic fluctuations of approximately 20-ps time scale can occur in methanol. The structural and optical consequences of these long timescale fluctuations are examined.