S. Kita

Repulsive potentials for Cl−–R and Br−–R (R=He, Ne, and Ar) derived from beam experiments

Repulsive potentials for Cl−–R and Br−–R (R=He, Ne, and Ar) have been derived from the experimental values of integral scattering cross sections of the ions in the energy range 0.5–4 keV. The potentials are well represented by an exponential form, V (R) =A exp(−αR). The numerical values of the parameters, A (eV) and α (A−1), are as follows: Cl−–He, 255, 2.88; Cl−–Ne, 820, 3.05; Cl−–Ar, 1470, 3.01; Br−–He, 365, 2.92; Br−–Ne, 985, 3.05; and Br−–Ar, 1420, 2.83. The potential parameters are found to be closely related to the electronic charge distributions in the colliding pairs on the assumption of overlapping of the electron clouds.

Repulsive potentials for Na+–R and Al+–R (R= rare gas atoms) derived from beam experiments

Repulsive potentials for Na+–R and Al+–R (R=rare gas atoms) are derived from integral scattering experiments using the projectile ions in the energy range 0.5–4 keV. The potentials are well represented by an exponential formula, V (R) =A exp(−αR). The numerical values of the parameters, A (eV) and α (A−1), are Na+–He, 1200, 4.92; Na+–Ne, 5350, 5.12; Na+–Ar, 11 340, 4.68; Na+–Kr, 9600, 4.33; Al+–He, 325, 3.50; Al+–Ne, 1220, 3.93; and Al+–Ar, 3170, 3.86. The statistical computation published by Kim and Gordon [J. Chem. Phys. 60, 4323 (1974)] for Na+–R is in good agreement with the experiments, and the values for Al+–He and Al+–Ar computed by a similar statistical method are also in good agreement with the experimental results, while Al+–Ne resulted in a significant discrepancy.

Experimental determination of repulsive potentials between alkali ions (Li+, Na+, and K+) and N2 and CO molecules

Abstract Integral scattering cross sections have been measured for alkali ions (Li + , Na + and K + ) in the energy range 500–4000 eV scattered by room temperature N 2 and CO molecules through effective laboratory angles greater than 5 × 10 −3 rad. The repulsive potentials deduced from the cross sections are represented bya practically identical formula for the Na + N 2 and Na + CO systems, and for the K + CO systems, respectively, while the repulsive potentials of the Li + N 2 system are somewhat smaller than those of the Li + CO system at larger intermolecular distances.

Some characteristics of pulsed nozzle beams

Some characteristic properties of pulsed nozzle beams produced with an automobile fuel injector were observed. A commercial fuel injector was modified to produce a beam pulse of a regular square shape. The beam pulse of 5 ms is again chopped by a slotted disk chopper to make a shorter burst at an arbitrary portion of the original pulse. Rotation of the disk chopper and actuation of the injector are synchronized by a microcomputer. Time‐of‐flight measurements were performed using beams of 15.6‐μs width formed in this way. Beam fluxes were measured with a flow‐through detector. The maximum beam fluxes and terminal speed ratios obtained for several gases in this work are comparable to the values published by other workers. Recoils of beam molecules from the skimmer and its vicinity significantly affect the quality of the pulsed beams.

Repulsive potentials derived from beam scattering of Rb+ and Cs+ ions by rare gas atoms

Integral cross sections of elastic scattering through effective LAB angles greater than 5×10−3 rad have been measured for collisions of Rb+ and Cs+ ions in the LAB energy range 500–4000 eV with room temperature rare gas atoms (He through Xe). Repulsive potentials in the range 0.5–10 eV derived from the results for the ion–atom pairs can be all expressed by exponential formulas. The potentials for Rb+–Ar, –Kr, and –Xe are in excellent agreement with the results derived from the mobility experiments by Gatland et al., but agreement between the two experiments for Cs+–Ar, –Kr, and –Xe are poor. The potential values calculated by Ishikawa et al. on the basis of the Gordon–Kim electron gas model are generally 20%–25% lower than the results of the present work.

Experimental determination of repulsive potentials between alkali ions (Li+, K+, and Cs+) and hydrogen molecules (H2 and D2)

Integral elastic scattering cross sections of alkali ions (Li+, K+, and Cs+) in collision with room temperature hydrogen molecules (H2 and D2) were measured in the ion energy range 500–4000 eV. Some difference in the cross sections due to the replacement of the target gases were found in K+‐ and Cs+‐hydrogen systems. Most of the difference can be explained by the difference of the target masses. The repulsive potentials deduced from the cross sections in a usual manner are represented by the following formulas independently of the isotopes: Li+: V(R) = 345 exp(−4.31 R), 0.88 < R < 1.43; K+: V(R) = 810 exp(−3.52 R), 1.33 < R < 1.98; and Cs+: V(R) = 1110 exp(− 3.26 R), 1.55 < R < 2.25; where V(R) is in units of electron volts and R in angstroms.

Experimental Determination of the Repulsive Potentials between Li^+ Ions and Rate-Gas Atoms

Integral elastic scattering cross sections of Li + ions scattered through effective laboratory angles greater than 5×10 -3 rad in collision with Ne, Ar, and Kr atoms at room temperatures were measured in the ion energy range of 500–4000 eV. The repulsive potentials derived from the cross sections are represented by the following analytical formulas:

Two-electron excitation and autoionisation processes in Na+-Ne collisions near threshold energy

By means of differential energy-loss measurements, autoionisation processes have been studied mostly at a centre-of-mass collision energy of E=93 eV, around which two-electron excitation due to potential curve crossing begins to arise. Additional experiments were done at E=107 and 163 eV. The velocity of the scattered particles was analysed by a time-of-flight technique. In the energy-loss spectra, two peaks of the autoionised Ne+ ions located at energy losses of Q approximately=45 and 37.5 eV were observed. The former loss peak is attributed to the reaction Na++Ne to Na++Ne(2s22p4(1D)3s2 1D)-45.2 eV Ne++e- and the latter peak can be interpreted in terms of the rainbow effect appearing in the molecular autoionisation process. The two-electron excitation process described above can be well understood as proceeding through two successive one-electron excitation processes Ne(2s22p6) to (Ne(2s22p53s)) to Ne(2s22p43s2).

Rainbow effects and momentum transfer mechanisms in collisions of Na+ ions with N2 and CO molecules

Rotational and vibrational excitations of molecules in Na+-N2 and Na+-CO collisions were studied at centre-of-mass energies of 27<or=E<or=192 eV. The energy of the scattered particles was analysed by a time-of-flight technique. The energy-loss spectra of the ions scattered in Na+-N2 collisions contain two peaks, while those for Na+-CO contain three peaks. The structures in the spectra can be well explained by rainbow effects arising from rotational and vibrational excitation.

Computation of Interaction Potentials between Closed-Shell Particles and between Open-Shell and Closed-Shell Particles

Computation based on the electron gas model for the interaction potentials between closed-shell particles was mode on M + -Xe (M + : Li + , Na + and K + ), Rb + -R and Cs + -R (R: rare gas atoms). The computation was also extended to some systems composed of open-shell and closed-shell particles, M + -H, M + -X and X + -R (X: C, N and O). The ion-diatom repulsion for M + -N 2 and M + -CO obtained on the basis of the dumbbell model with the ion-atom potentials is in good agreement with experimental results.