IMPURITY PHOTOCONDUCTION, EXCITONS, AND EFFECTIVE MASSES IN LIQUID XENON

Photoconductivity excitation spectra in liquid xenon doped by methyl iodide or toluene were recorded for a broad range of impurity concentrations (5 ppm-1.1%) and xenon densities ranging from the critical point to the triple point. Electrons liberated from the impurity molecules yield photocurrent in a broad spectral range, with excitonic transitions of the xenon host appearing as dips on a continuous background. It is demonstrated that, with the experimental conditions employed, the reciprocal values of the photocurrent represent fairly well the absorption spectrum of the host. Such reciprocal spectra enabled us to determine the parameters of the n = 2 Mott-Wannier exciton for densities-rho ranging from 9.5 to 13.6 X 1O(21) cm-3. From these, in turn, along with previously determined intrinsic photoconduction threshold values, the electron effective mass m(e) was determined as almost-equal-to 0.28m (m being the free-electron mass) in the whole range of densities, with indication for a shallow broad minimum at rho-almost-equal-to 11 X 10(21) cm-3.