Electron spectra for associative detachment in low-energy collisions of Cl and Br with H and D^†

Abstract

Energy spectra of electrons detached in collisions of Cl − and Br − with atomic hydrogen and deuterium have been measured for laboratory frame ion energies between 0.2 and 8.0 eV. Their shapes agree very well with the predictions of nonlocal resonance theory. Both types of structure predicted by the theory are observed. They are the 'v steps', at ro-vibrational thresholds, and the 'S steps', which are a consequence of interchannel coupling,which raises the cross section when a higher vibrational channel closes. They exhibit the behaviour predicted by theory both when the collision energy is varied and upon isotope substitution. The 'v steps' move to higher electron energies with higher collision energy and when hydrogen is substituted by deuterium, reflecting the higher maximum energy available to the electron. The positions of the S steps do not depend on collision energy, and are essentially equal to differences of vibrational energies of the product molecules HCl, DCl, HBr and DBr. The relative cross sections for formation of low vibrational levels (i.e., emission of fast electrons) are smaller in the deuterated compounds, reflecting the slower motion of D compared to H and consequently preferred detachment at high internuclear separations.

Isotope effect for associative detachment:H(D)−+H(D)→H2(Miller1, Bruhns2, Čı́žek3 et al. 2012Phys. Rev. A312240View full textAdd to dashboardCite

“…For the same collision energy, D moves more slowly than H and penetrates less deeply into the electron cloud of the anion before detachment occurs. The resulting deuterated molecule forms at higher internuclear distances and higher vibrational levels than for the undeuterated molecule [5]. This was seen by the only experimental AD studies we know of which investigate the isotope effect for two-atom collision systems [5,6].…”

“…The resulting deuterated molecule forms at higher internuclear distances and higher vibrational levels than for the undeuterated molecule [5]. This was seen by the only experimental AD studies we know of which investigate the isotope effect for two-atom collision systems [5,6]. In [5] experimental and theoretical work was carried out for AD of H and D with Cl − and Br − by measuring the relative cross section as a function of the detached electron energy.…”

“…This was seen by the only experimental AD studies we know of which investigate the isotope effect for two-atom collision systems [5,6]. In [5] experimental and theoretical work was carried out for AD of H and D with Cl − and Br − by measuring the relative cross section as a function of the detached electron energy. For AD of H + F − and D + F − [6] the relative vibrational level v populations of the resulting HF and DF were determined by measuring the infrared spectra from the excited ro-vibrational states.…”

A novel merged beams apparatus to study anion-neutral reactions

“…[28][29][30] Over the past 40 years a number of techniques have been developed and used to study anion-neutral chemistry. These methods include flowing afterglow and its successors, [31][32][33] as well as ion traps, 34,35 crossed beams, 8,36,37 and guided ion beams. 38,39 A wide range of anion-neutral reactions have been studied using these techniques and much has been learned.…”

“…Hence, the overlap of the two beams cannot be reliably determined and this technique produces only relative cross section results. 8,36,37 Guided ion beams send anions through a target gas cell of known density and measure the product anions. Laboratory beam energies are in the ϳmeV to eV range.…”