Electron Loss in Low-EnergyH+-H(high n)Merged-Beam Collisi

Abstract

We have measured the electron-loss cross section for collisions between protons and highly excited hydrogen atoms having principal quantum numbers in the nominal n band 44%n% 50. The cm. collision energy range was 0.4 eV^ pp^ 61 eV. Theoretical ionization-cross-section results are compared with the data and are then used to unfold from the data the approximate electron-transfer cross section. Classical scaling calculations are found to be in reasonable agreement with the unfolded data while quantal predictions are not.The comparison of experiment and theory for H*-H(n) collisions leading to electron loss, the sum of electron transfer and ionization, has been limited to the one restricted case of principal quantum number n = l. 1 Although theory exists, the n dependence of the electron-loss cross section has never been measured in any collision energy range, either in this most fundamental ionatom system or in any other.The electron-transfer and ionization cross sections for low-energy (eV energy range) H + -H(high n) collisions are among those required for evaluation of the important role that electron-capture and -loss collisions involving excited states may have in affecting the transport properties of plasmas. 2 Astrophysically these collisions are believed to be important in the ionized-hydrogen (H II) regions in interstellar space. 3 It is the purpose of this Letter to report results of the first experimental study of H + -H(high n) collisions. The merged-beam electron-loss cross-section data cover the center-of-mass collision-energy range 0.4 eV< W^ 61 eV; the H(high n) target atoms had quantum numbers n in the nominal n band 44 % n % 50.The transition from "low"-to "high"-energy behavior of electron-transfer and ionization cross sections in ion-atom collisions occurs when the velocity v r of relative motion of the nuclei is comparable with the orbital velocity v" of the electron taking part in the collision. For H + -H(n) collisions, v r~v n when W^ 1.3x 10 4 n~2 eV. For n = l, this occurs at W^ 13 keV; forn = 47, at W ^6 eV. The cross-section data reported in this Letter cover both the low-and high-energy regions.The measurements were performed with a new, single-ion-source, merged-beam apparatus incorporating significant technological advances. The method is based on that introduced by Belyaev, Brezhnev, and Erastov. 4 Part of the apparatus is shown in Fig. 1. A pure H + beam with energy E B near 11 keV and energy spread measured to be % ± 20 eV around E B was generated with an rf ion source, accelerator, and mass analyzer system not shown in Fig.

An Inequality of Jackson Type for Abstract Functions

“…Charge transfer cross sections involving electronically excited atoms are, however, known to be considerably larger. For example, Koch and Bayfield [19] studied the reaction H + +H(n = 47) and found an electron transfer cross section of the order of 10 6 -10 7Å2 compared with 30Å 2 for the ground state [20]. Thus, we conclude that the dominating process of formation of the atoms with hyper-thermal velocity is a charge transfer reaction in which electronically excited species are involved.…”

Attosecond-scale dynamics in ion–atom collision versus laser–atom interaction

“…We have shown that, for a good matching, one must add capture and ionization probabilities for the collision process to compare with the case of optical pulses. The electron loss defined can be measured experimentally, see for example [30]. Moreover, we have seen that the key parameter for the design of the pulses is energy, and not its duration.…”

Recent advances in the chemistry of Rh carbenoids: multicomponent reactions of diazocarbonyl compounds

“…A furnace target technique employing electric field ionization to detect excited collision products has been used by Bayfield et al [96] to determine cross-sections for capture into highly excited states of H in the process H'+H -+ H ( 1 3 < n < 2 8 ) + H + (10) Measured cross-sections in the range 7-60 keV for capture into all states between n = 13 and 28 attain a maximum value of about 7 x 10-'9cm2 at about 30keV. Roy et al [97] have shown that while the experimental cross-sections above 50 keV are much smaller than values predicted by the Oppenheimer-Brinkman-Kramers approximations, a satisfactory description is provided by calculations based on the approximations of Jackson and Schiff [98], Bassel and Gerjuoy [99] and Band [loo].…”