Selective-Excitation Study of Collisional Excitation Transfer for Helium 31,3P and D States

By observing the time-resolved fluorescence following the laser excitation of a helium level in a discharge plasma, the authors have determined the excitation transfer rate coefficients among the n =3 levels due to atomic and electronic collisions. The result in the form of the thermally averaged cross section is: for 3 1 P→3 1 D <σ atom >=(1.9±0.4)×10 -15 cm 2 and <σ elec. >=(2.4±1.2)×10 -13 cm 2 ; for 3 3 D→3 3 P <σ atom >=(5.3±1.2)×10 -17 cm 2 and <σ elec. >=(0.9±0.4)×10 -13 cm 2 . The cross sections for atomic collisions are in reasonably good agreement with other experimental and theoretical data, but the cross sections for electronic collisions are larger than the earlier experimental data by two orders and are extremely good agreement with the recent calculations.