Cross Sections For Mutual Neutralization Research Articles

Studies of mutual neutralization in collisions involving Mg+/H−, Na+/H−, Li+/H− and Li+/Cl−

The Landau-Zener model is used to systematically compute mutual neutralization cross sections for collisions between Mg+/H−, Na+/H−, Li+/H− and Li+/Cl−. Potential energy curves for electronic states that are relevant for mutual neutralization are taken from available literature. Where non-adiabatic couplings are available, they are utilized to compute the diabatic potential energy curves, crossing distance and electronic couplings. In cases where non-adiabatic couplings are not available, they are approximated using a Lorentzian function. The reaction cross sections are computed for the energy range 0.001 eV to 1000 eV. The results are compared with other available experimental and theoretical results and are found to be very comparable. There is an observable trend in the reaction cross section involving ions of metals and hydrogen at collision energies below 10 eV, with the heaviest metal showing the largest reaction cross section and the lightest metal with the lowest cross section. At collision energies below 10 eV, isotope effect is also found to have an effect on the reaction cross section for Li+/Cl−.

Correspondence between the surface integral and linear combination of atomic orbitals methods for ionic-covalent interactions in mutual neutralization processes involving H−/D−

The surface integral method for estimating ionic-covalent interactions in diatomic systems been successful in producing cross sections for mutual neutralization (MN) in reasonable agreement with experimental results for branching fractions between final states in systems such as ${\mathrm{O}}^{+}\text{/}{\mathrm{O}}^{\ensuremath{-}}$ and ${\mathrm{N}}^{+}\text{/}{\mathrm{O}}^{\ensuremath{-}}$. However, for simpler cases of MN involving ${\mathrm{H}}^{\ensuremath{-}}$ or ${\mathrm{D}}^{\ensuremath{-}}$, such as ${\mathrm{Li}}^{+}\text{/}{\mathrm{D}}^{\ensuremath{-}}$ and ${\mathrm{Na}}^{+}\text{/}{\mathrm{D}}^{\ensuremath{-}}$, it has not produced results that are in agreement with experiments and other theoretical calculations; in particular, for ${\mathrm{Li}}^{+}\text{/}{\mathrm{D}}^{\ensuremath{-}}$ calculations predict the wrong ordering of importance of final channels, including the incorrect most populated channel. The reason for this anomaly is investigated, and a leading constant to the asymptotic ${\mathrm{H}}^{\ensuremath{-}}$ wave function is found that is different by roughly a factor of $1\text{/}\sqrt{2}$ from that which has been used in previous calculations with the surface integral method involving ${\mathrm{H}}^{\ensuremath{-}}$ or ${\mathrm{D}}^{\ensuremath{-}}$. With this correction, far better agreement with both experimental results and calculations with full quantum and linear combination of atomic orbitals (LCAO) methods is obtained. Further, it is shown that the surface integral method and LCAO methods have the same asymptotic behavior, in contrast to previous claims. This result suggests the surface integral method, which is comparatively easy to calculate, has greater potential for estimating MN processes than earlier comparisons had suggested.

Mutual neutralization in collisions of H+ with Cl.

The cross section and final state distribution for mutual neutralization in collisions of H+ with Cl- have been calculated using an ab initio quantum mechanical approach. It is based on potential energy curves and nonadiabatic coupling elements for the six lowest 1Σ+ states of HCl computed with the multireference configuration interaction method. The reaction is found to be driven by nonadiabatic interactions occurring at relatively small internuclear distances (R < 6 a0). Effects on the mutual neutralization cross section with respect to the asymptotic form of the potential energy curves, inclusion of closed channels, as well as isotopic substitution are investigated. The effect of spin-orbit interaction is investigated using a semiempirical model and found to be small. A simple two-state Landau-Zener calculation fails to predict the cross section.

Mutual Neutralization in Li+−D− Collisions: A Combined Experimental and Theoretical Study

Abstract We present a combined experimental and theoretical study of the mutual neutralization (MN) process in collisions of lithium ions (Li+) with deuterium anions (D−) at collision energies below 1 eV. We employ a merged-beam apparatus to determine total and state-to-state MN cross sections. We perform nuclear dynamics calculations using the multichannel Landau–Zener model based on accurate ab initio molecular data. We obtain an excellent agreement between the experimental and theoretical results over the energy range covered in this work. We show that the basis sets used in the ab initio calculations have a limited influence on the total cross section, but strongly impacts the results obtained for the partial cross sections or the reaction branching ratios. This demonstrates the important role of high-precision measurements to validate the theoretical approaches used to study gas-phase reactive processes. Finally, we compute MN rate coefficients for Li+ + H− and Li+ + D−, and discuss their significance for astrochemistry models.

Theoretical study of mutual neutralization inHe++H−collisions

Total and differential cross sections for mutual neutralization in ${\mathrm{He}}^{+}$ and ${\mathrm{H}}^{\ensuremath{-}}$ collisions at low to intermediate (0.001 eV to 100 eV) are calculated ab initio and fully quantum mechanically. Atomic final-state distributions and isotope effects are investigated. The theoretical model includes dynamics on eleven coupled states of $^{2}\mathrm{\ensuremath{\Sigma}}^{+}$ symmetry, where autoionization is incorporated. The potential-energy curves, autoionization widths, and nonadiabatic couplings of electronic resonant states of HeH are computed by combining structure calculations with electron scattering calculations. The nuclear dynamics is studied using a strict diabatic representation of the resonant states. Effects of rotational couplings between $^{2}\mathrm{\ensuremath{\Sigma}}^{+}$ and $^{2}\mathrm{\ensuremath{\Pi}}$ electronic states are investigated in the pure precession approximation.

Mutual neutralization in collisions of Li + and F −

Abstract Mutual neutralization in collisions of Li+ and F− is driven by an avoided crossing between the two lowest 1 Σ + electronic states of the LiF system. These electronic states are computed using the multi-reference configuration interaction method. We investigate how the adiabatic potential energy curves and the non-adiabatic coupling element depend on the choice of the reference configurations as well as the basis set. Using diabatic states, the total and differential cross sections for mutual neutralization are computed.

Mutual neutralization in slow H+2−H− collisions

The process of mutual neutralization in slow H+2+H− collisions is considered within the multi-channel Landau–Zener model. The cross sections for electron capture from H− to specific gerade (singlet and triplet) states of H2 molecule are calculated in the CM energy range from 0.05 keV/u to 5 keV/u. The calculated total mutual neutralization cross section is in satisfactory agreement with the experimental data available in the CM energy range 20–2000 eV.

Merged-beam measurements of the mutual neutralization of ions

A merged-beam apparatus has been used to measure cross sections for mutual neutralization for centre-of-mass energies between 3 and 460 eV. Different ion sources and gas mixtures were used to vary the vibrational state population of the ions and the cross section appears to be insensitive to the initial vibrational state. The measurements differ significantly from the results of a recent calculation but, at interaction speeds greater than about , converge with results for the atomic ion pairs , , and .

Coulomb trajectory effects on electron-impact detachment of negative ions and on mutual neutralization cross sections

Cross sections of electron-impact detachment of negative ions and of mutual neutralization between positive and negative ions are calculated using a model based on the semiclassical theory for ion - atom collisions but modified to include Coulomb trajectory effects. It is shown that the method allows us to obtain accurate results for collisions down to low energies. The Coulomb repulsion between the electron and the negative ion accounts for the rapid decrease of detachment cross sections at low energies, and the Coulomb attraction between positive and negative ions accounts for the rapid increase of neutralization cross sections at low velocities.

Mutual Neutralization of Na+/O- Ions in Slow Collisions

The mutual neutralization cross sections of Na+/O- ions at low energy have been calculated by using the multichannel Landau-Zener theory. An asymptotic method is used for estimating the coupling matrix elements between the ionic and covalent states at the crossing points of diabatic potential curves. The results of calculation are compared with available experimental data.

Cross section for the mutual neutralization reaction H2++H-, calculated in a multiple-crossing Landau-Zener approximation.

A multiple-crossing Landau-Zener model is applied to calculate mutual neutralization cross sections for the reactions ${\mathrm{H}}^{+}$+${\mathrm{H}}^{\mathrm{\ensuremath{-}}}$ and ${\mathrm{H}}_{2}^{+}$+${\mathrm{H}}^{\mathrm{\ensuremath{-}}}$ as a function of the principal quantum number n of the resulting H atom. For low-energy collisions (E\ensuremath{\le}10 eV), the total cross section for ${\mathrm{H}}_{2}^{+}$+${\mathrm{H}}^{\mathrm{\ensuremath{-}}}$ is a factor of 8 larger than the one for ${\mathrm{H}}^{+}$+${\mathrm{H}}^{\mathrm{\ensuremath{-}}}$. The cross section for the process including ${\mathrm{H}}_{2}^{+}$, in which the H atom is excited to the quantum state n (2\ensuremath{\le}n\ensuremath{\le}8), has a nonmonotonic behavior as a function of the atomic quantum state. Comparison of the calculated results with newly received experimental data is made.

Merged beam measurements of the mutual neutralization of He+/H- and Li+/D- ions

Mutual neutralization cross sections for He+/H- and Li+/D- have been measured by a merged beam technique for centre of mass energies between 0.6 and 300 eV. The results are in good agreement with previous inclined and merged beam measurements and with recent theory, all of which only covered energy ranges above 30 eV. At interaction speeds greater than about 3*105 m s-1 results for H+/H-, He+/H-, Li+/H- and Li+/D- all converge.

Mutual neutralization and chemiionization in collisions of alkali metal and halogen atoms

A semiempirical valence bond method is used to obtain realistic potential curves for the three lowest 1∑+ curves of NaF, KF, LiCl, NaCl, KCl, Lil, and Nal. They are used together with a model functional form for the diabiatic coupling to compute quantal chemiionization and mutual neutralization cross sections. The accuracy of one-electron estimates of the interaction energies in the crossing regions is explored. The Landau–Zener method is found to be very reliable except for collisions involving iodine, for which modifications are necessary.

Molecular-state cross-section calculations for H+Na

Pseudopotential molecular-structure calculations have been used to obtain the seven lowest $^{1}\ensuremath{\Sigma}$ and $^{1}\ensuremath{\Pi}$ states of CsH. These states and their associated radial and rotational coupling terms have been used to calculate the cross sections for ${\mathrm{H}}^{\ensuremath{-}}$+${\mathrm{Cs}}^{+}$ ion-pair production in $\mathrm{H}+\mathrm{Cs}(6s)$ and $\mathrm{H}+{\mathrm{Cs}}^{*}(6p)$ collisions at energies from 0.1 to 10 keV. The ion-ion mutual neutralization cross section, ${\mathrm{H}}^{\ensuremath{-}}$+${\mathrm{Cs}}^{+}$ \ensuremath{\rightarrow} H+Cs, is also presented. The cross-section calculations were done with the perturbed-stationary-state method, modified to include two-electron translation factors. The ion-pair production cross section for ground-state reactants is in good agreement with experiment; collisions of H with excited ${\mathrm{Cs}}^{*}(6p)$ show an order-of-magnitude enhancement of the ion-pair production cross section at 100 eV. The ion-ion mutual neutralization cross section is found to be large, attaining a value of 1.3 \ifmmode\times\else\texttimes\fi{} ${10}^{\ensuremath{-}14}$ ${\mathrm{cm}}^{2}$ at 0.1 keV.

Molecular-state cross-section calculations for H+Cs⇄H−+Cs+

Pseudopotential molecular-structure calculations have been used to obtain the seven lowest $^{1}\ensuremath{\Sigma}$ and $^{1}\ensuremath{\Pi}$ states of CsH. These states and their associated radial and rotational coupling terms have been used to calculate the cross sections for ${\mathrm{H}}^{\ensuremath{-}}$+${\mathrm{Cs}}^{+}$ ion-pair production in $\mathrm{H}+\mathrm{Cs}(6s)$ and $\mathrm{H}+{\mathrm{Cs}}^{*}(6p)$ collisions at energies from 0.1 to 10 keV. The ion-ion mutual neutralization cross section, ${\mathrm{H}}^{\ensuremath{-}}$+${\mathrm{Cs}}^{+}$ \ensuremath{\rightarrow} H+Cs, is also presented. The cross-section calculations were done with the perturbed-stationary-state method, modified to include two-electron translation factors. The ion-pair production cross section for ground-state reactants is in good agreement with experiment; collisions of H with excited ${\mathrm{Cs}}^{*}(6p)$ show an order-of-magnitude enhancement of the ion-pair production cross section at 100 eV. The ion-ion mutual neutralization cross section is found to be large, attaining a value of 1.3 \ifmmode\times\else\texttimes\fi{} ${10}^{\ensuremath{-}14}$ ${\mathrm{cm}}^{2}$ at 0.1 keV.

Mutual neutralization in rare gas halides

The cross sections for mutual neutralization in Ne++F−, Ar++F−, and K++Cl are obtained from two-state close coupling calculations. The Landau–Zener approximation gives adequate results in each case. The rate of neutralization is studied as a function of ambient gas density. Near atmospheric pressure, mutual neutralization is more likely than excimer formation of Ne++F− collisions, but less likely in Ar++F− collisions.

Measurements of cross sections for the mutual neutralization of H+and H-ions

An apparatus has been constructed to observe various interactions between ions. In the present experiment, beams of H+ and H- ions intersected at 81/2 degrees and cross sections for mutual neutralization were measured for barycentric energies between 20 and 3000 eV. The earlier results of Gaily and Harrison (1970) and Moseley et al. (1970) were closely confirmed, but the greater accuracy of the new measurements made it possible to resolve maxima in the cross section curve around 32 and 54 eV. Two further maxima at 120 and 600 eV had previously been observed by Gaily and Harrison.

H++H−Mutual Neutralization Cross Section Obtained with Superimposed Beams

The ion-ion mutual neutralization cross section for ${\mathrm{H}}^{+}$ + ${\mathrm{H}}^{\ensuremath{-}}$ has been measured over the barycentric energy range from 0.15 to 300 eV using a merged-beam technique. The results are compared with theoretical calculations and with a recent higher energy experimental measurement. An estimate of the thermal rate coefficient is made.

Ion-Ion Mutual Neutralization Cross Sections Measured by a Superimposed Beam Technique

Ion-ion neutralization cross sections have been measured for ${\mathrm{N}}^{+}$ + ${\mathrm{O}}^{\ensuremath{-}}$, ${\mathrm{N}}_{2}^{+}$ + ${\mathrm{O}}_{2}^{\ensuremath{-}}$, and ${\mathrm{O}}_{2}^{+}$ + ${\mathrm{O}}_{2}^{\ensuremath{-}}$. The kinetic energy range, in the barycentric coordinate system covered by the experiment, is between 0.1 and 98 eV with an energy resolution of about 0.1 eV. The products of the neutralization cross section $Q$ times the relative speed ${v}_{\mathcal{r}}$ are nearly independent of energy, having values close to ${10}^{\ensuremath{-}7}$ ${\mathrm{cm}}^{3}$/sec for all three systems studied, except that below 0.5 eV the ${\mathrm{N}}^{+}$ + ${\mathrm{O}}^{\ensuremath{-}}$ and ${\mathrm{N}}_{2}^{+}$ + ${\mathrm{O}}_{2}^{\ensuremath{-}}$ systems show a rapid increase of $Q{v}_{\mathcal{r}}$ with decreasing energy. The experiment employs the superposition of positive- and negative-ion beams of several keV energy over a common path length of 33 cm. The beams are subsequently separated and the neutral products of the reaction are measured.