Collisional Excitation Transfer to the4D1State in Helium by Multiple State Mechanism

The electron-excitation function of the $4{}_{}{}^1{}_{}{}^{}D$ state of helium has been measured at various pressures by means of an automatic processing system. The peak of the curve shifts gradually from 50 eV to 100 eV as the pressure is increased due to the collision transfer from the ${}_{}{}^1{}_{}{}^{}P$ states. The transfer can be explained by the multiple state mechanism. Based on this theory the calculated population of the $4{}_{}{}^1{}_{}{}^{}D$ state at 7.4×${10}^{-2\mathrm{}}$ mm pressure agrees quite well with experiments. The observed amount of transfer from $\mathrm{n}{}_{}{}^1{}_{}{}^{}P$ states to $4{}_{}{}^1{}_{}{}^{}D$ and to $4{}_{}{}^3{}_{}{}^{}D$ are of the same order of magnitude as predicted by the theory. The results of this work provide strong support for the multiple state transfer process.