Collisional transfer rates between excited levels in helium

In an electron-beam plasma selective excitation by pulsed-dye-laser pumping has been used to study excitation transfer by electronic collisions. In particular, rate coefficients for the transitions $4{}_{}{}^1{}_{}{}^{}P\to 4{}_{}{}^1{}_{}{}^{}S$ and $3{}_{}{}^1{}_{}{}^{}P\to 3{}_{}{}^1{}_{}{}^{}S$ have been derived as well as the total deexcitation rate coefficient by $\Delta n\ne 0$ collisions of the $4{}_{}{}^1{}_{}{}^{}P$ and $4{}_{}{}^3{}_{}{}^{}D$ levels. The agreement with theoretical values is within the experimental uncertainties. The effective excitation transfer between the $n=4\mathrm{}$ singlet and triplet levels is higher than expected by about two orders of magnitude.