Dissociative attachment of low-energy electrons to state-selected diatomic molecules

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The dissociative attachment process in low-energy collisions [Na{sub 2}({ital v}{sup {double_prime}},{ital j}{sup {double_prime}})+{ital e}{sup {minus}}{r_arrow} Na + Na{sup {minus}}, with electron energies {lt}1.0 eV] is studied as a function of vibrational excitation over a broad range of excited levels. We employ a crossed electron-molecule beams arrangement and two optical methods for preparing vibrationally excited states: Franck-Condon pumping (FCP) as well as the efficient and highly state-specific technique of stimulated Raman scattering with adiabatic passage (STIRAP). Both methods are capable of preparing vibrational levels with energies up to about 60{percent} of the Na{sub 2}{ital X}{sup 1}{Sigma}{sub {ital g}}{sup +} binding energy ({ital v}{sup {double_prime}}{le}30). Analysis of the FCP data shows an increase of more than three orders of magnitude in the state-dependent dissociative attachment rate as a function of the vibrational level up to {ital v}{sup {double_prime}}=12. For {ital v}{sup {double_prime}}{approx_gt}12, which is close to the exoergic threshold, no further increase with {ital v}{sup {double_prime}} is observed. The dissociative attachment rates measured for single rovibronic states using the STIRAP technique confirm the validity of the conclusions drawn from our analysis of the FCP measurements. The potential curve of the Na{sub 2}{sup {minus}}{ital A}{sup 2}{Sigma}{sub {ital g}}{sup +} state, which is essentialmore » for the dissociative attachment process, has been determined from variational valence shell multireference configuration interaction calculations in its bound region but by imposing Feshbach projection in its resonance region. The crossing of this potential with that of the Na{sub 2}({ital X}) state is found between {ital v}{sup {double_prime}}=11 and {ital v}{sup {double_prime}}=12, in full agreement with the conclusions from analysis of the experimental data. (Abstract Truncated)« less