Excess electronic states in fluid helium

Abstract

We study the nature of the excess electronic states in fluid helium by calculating the excess electron energies and wave functions for a set of configurations of solvent atoms taken from path integral Monte Carlo calculations on the solvated electron system. The eigenvalues and eigenfunctions for the different configurations of the solvent are used to calculate the inhomogeneously broadened density of states and absorption line shape of the excess electron over a range of fluid densities. The predictions of a simple theory of the excess electronic states in fluid helium due to Springett et al. [B. E. Springett, M. H. Cohen, and J. Jortner, Phys. Rev. 159, 183 (1967)] are found to agree quite well with our computer simulation results. This simple theory, however, predicts an inhomogeneously broadened elecronic absorption linewidth which is much narrower than that obtained from simulation. It is found that the RISM-polaron theory of Nichols and Chandler [A. L. Nichols III and D. Chandler, J. Chem. Phys. 87, 6671 (1987)] gives an absorption line shape which is in better agreement with our simulations. We observe a transition from lower energy states in which the electron is bound to density fluctuations in the fluid to the situation where the excess electron scatters through the fluid in continuum states at higher energies.