In a multi-keV temperature deuterium plasma such as JET, CVI emission arises from collision processes which, in the absence of neutral deuterium beam heating, occur near the plasma boundary. Distortions to the CVI Lyman decrement. such as the Ly β/γ/δ ratio and enhancement of the high quantum states (n~12) are observed. These are correlated to the Dα intensity and consequently to the influx of Do atoms at the plasma boundary. The intensities of the Lyman spectra are interpreted in terms of low energy electron transfer from thermal Do atoms to C+6 ions as well as electronic excitation of 6+5 ions in their ground state. The line-of-sight emission is modelled using an impurity ion transport code with input data on the electron and Do profiles. Electron transfer from excited states of Do (up to the thermal limit) as well as the ground state have to be included to give satisfactory agreement with the CVI Lyman spectra when the Do influx is high. The cross-sections for charge-transfer from excited states have been estimated using a simple Landau-Zener model. Comparison of the relative intensities of the CVI Lyman series Ly β/γ/δ etc with the model calculations allows plausible corrections to be made to the effective charge transfer cross-section as a function of principle quantum number. The observations offer a potential method of measuring local Do concentrations near the boundary of high temperature, high Do recycling plasmas, but limited at present by the uncertainties of low energy charge transfer cross-sections.