The Ha (Da) line shape in front of the limiter and the wall is measured by two sets of optical spectroscopy multichannel analysers. The energy distribution is derived directly from the Ha (Dα) line shape, especially showing several molecular processes. The dissociative excitation of molecules is dominating when the local electron temperature is above 10eV. The Dα line shape is also simulated by the Monte Carlo method, the result shows that the molecular dissociation contributes 57% neutral atoms, 53% emission intensity in front of the limiter, and 85% neutral atoms, 82% emission intensity in front of the wall. The power loss from molecular dissociation is about 5.6×104 kW/m-3 and the molecular dissociation is an important cooling mechanism at the plasma edge.