Questioning the observation of laser-assisted ionization in fast collisions ofHe/emph>(21,3S) with He

In four recent papers Pradel et al. [Phys. Rev. Lett. 54, 2600 (1985); Phys. Rev. A 35, 1062 (1987)] and Monchicourt et al. [Phys. Rev. A 33, 3515 (1986); Chem. Phys. Lett. 152, 336 (1988)] give arguments claiming the observation of laser-assisted ionization of the short-lived collision complex formed during collisions of ${\mathrm{He}}^{\mathrm{*}}$(2 ${}_{}{}^1{}_{}{}^{}$,3S) with He. However, estimates of the relative sizes of the assisted and unassisted ion signals observed make it very unlikely that laser-assisted ionization has been observed in those experiments. Collisional excitation to higher ${\mathrm{He}}^{\mathrm{*}}$ states, followed by (single-photon) ionization of the excited states, seems a more likely explanation at all energies considered.