Production of D* (n = 4) from electron-D2+ dissociative recombination

Crossed beams of electrons and D₂⁺ ions were used to measure absolute cross sections for the dissociative recombination process, e+D₂⁺(X ²Σ_g⁺)->D+D^*(n=4) over a range of electron energies extending from 0.6 to 7 eV. The process was monitored by detecting a known portion of the 485.9-nm emission resulting from radiative decay of the product D^*(n=4) atoms. The cross sections, which correspond to a known vibrational-state distribution of the target ions, exhibit the same dependence on electron energy as recent measurements of the total dissociative recombination cross section reported by Peart and Dolder, and have a magnitude of about 10% of the total cross section, suggesting that the product D atoms are formed in excited states with a variety of principal quantum numbers. Systematic measurement uncertainties at high confidence are about 14%, and random uncertainties are at the 25% (standard deviation) level. The calculation of cross sections from the observed light intensities depends on the mean lifetimes and branch ratios for 485.9-nm emission, whose evaluation in turn requires assumptions concerning the recombination process. The situation is complicated by the presence of an electron-beam-confining magnetic field in the collision volume, which causes the incident ions and product atoms to experience a transverse motional electric field. A time-independent perturbation calculation of the weak-field Stark and Zeeman effects was performed and mean lifetimes and branch ratios were estimated under different assumptions concerning the recombination process. Assuming that all perturbed product n=4 states are equally populated by dissociative recombination yields an experimental cross section of 1 × 10⁻¹⁶ cm² at 0.7 eV, decreasing to 3.3 × 10⁻¹⁷ cm² at 3 eV, and to 1 × 10⁻¹⁷ cm² at 7 eV. Assuming that only the perturbed 4s states are initially populated results in cross sections larger by some 50%.