J. E. Jordan

Scattering of High‐Velocity Neutral Particles. XIV. He–He Interaction below 1.1 Å

Total elastic cross sections have been measured for helium atoms within energies between 300 and 2000 eV which have been scattered by room‐temperature helium through an effective laboratory angle greater than about 1×10−2 rad. Special features and procedures used in the experiments include the use of a magnetic field to increase the positive‐ion current in the source, acceleration of the positive ions extracted from the source in a region of relatively low pressure with a consequent reduction in their energy spread, production of neutrals by charge transfer in a chamber separated from the scattering chamber, modulation of the neutral beam to produce an ac signal on a compensated thermal detector, and amplification of the detector signal with synchronous rectification, at the modulation frequency, of the amplifier output.A detailed analysis of the scattering results treats effect on the measured cross sections of the intensity distribution in the beam and of the beam‐detector geometry, interpretation of th...

Scattering of High Velocity Neutral Particles. X. He–N2; A–N2. The N2–N2 Interaction

Total collision cross sections have been measured for helium atoms with energies between 500 and 2100 ev, and for argon atoms with the same energies, scattered in room temperature nitrogen. The results have been analyzed to obtain the average potential between a helium atom and a nitrogen molecule, 〈V(r)〉Av=1.19×10−10/r7.06 ergs, for r between 1.79 A and 2.29 A, and the average potential between an argon atom and a nitrogen molecule, 〈V(r)〉Av=1.21×10−9/r7.78 ergs, for r between 2.28 A and 2.83 A.A procedure which takes into account the noncoincidence of the center of mass and the centers of force in the N2 molecule has been developed for expressing these average atom‐molecule interactions as functions of the atom‐atom potential between the beam particle and either of the nitrogen atoms. These interatomic potentials have been combined with potentials previously determined for He–He and A–A to obtain a hypothetical potential between two nitrogen atoms in different N2 molecules. The following average intermo...

Scattering of High‐Velocity Neutral Particles. XI. Further Study of the He–He Potential

Results are presented for two studies of the scattering by room‐temperature helium of beams of helium atoms with controlled energies in the approximate range 150–1500 ev. The interaction potential derived from the two sets of measurements is represented by φ(r)=5.56×10−12/r5.03 erg  (0.97 A<r<1.48 A). Where there are common ranges of the interaction distance r this potential is in reasonable agreement with He–He potentials previously determined from scattering experiments. In its specified range of validity, it is somewhat lower than most of the corresponding values calculated quantum mechanically.

Scattering of High‐Velocity Neutral Particles. XVII. Ar–O2, Ar–N2, Ar–CO

Fast Ar beams with energies between about 200–1500 eV have been scattered by room‐temperature O2, N2, and CO to obtain the following potentials (where the energy is given in electron volts and the interaction distance in angstroms): Ar–O2 V(r) = 1.36 × 103 / r8.34 2.01 < r < 2.50, Ar–N2 V(r) = 567 / r7.06 2.04 < r < 2.53, Ar–CO V(r) = 551 / r6.99 2.09 < r < 2.68. Results for these systems in the indicated ranges have not been previously reported from this laboratory. They are, however, in quite satisfactory agreement with independent measurements of Leonas and coworkers in Moscow, and show that even at the small separation distances involved in these high energy collisions, the average force fields on N2 and CO are essentially identical. The peripheral‐force approximation, which assumes that the centers of force in a molecule are located at the nuclei of each atom, has been used to construct the individual atom–atom interactions which combine to make up the experimental atom–molecule potentials. In the on...

Scattering of Fast Potassium Ions by Helium, Neon, and Argon

A new apparatus has been designed and built, and measurements have been made of the effective total cross sections for the scattering of potassium ions with energies between 150 and 2350 eV by room temperature helium, neon, and argon. The repulsive interaction potentials were deduced from the measured cross sections with two different representations of the potential, the inverse power, and the exponential. The results are as follows (energies are in electron volts and distances are in angstroms): K+–HeV(r)=27.0/r6.22,V(r)=2200 exp(−4.56r),1.18 ≤ r ≤ 1.83,K+–NeV(r)=122/r7.64,V(r)=7850 exp(−4.79r),1.42 ≤ r ≤ 2.02,K+–ArV(r)=667/r7.78,V(r)=8900 exp(−3.96r),1.76 ≤ r ≤ 2.47. These results compare very favorably with other experimental potentials reported recently but are in sharp disagreement with some earlier results. They also disagree with reported potentials which were calculated theoretically, except for the case of K+–Ar where the agreement between theory and experiment is remarkably good. The potentials...

Scattering of high‐velocity Ar atoms by CO2, OCS, and CS2

Fast Ar beams have been scattered by room‐temperature CO2, OCS, and CS2 to obtain average atom–molecule potentials. The results are consistent with other scattering measurements on similar systems, and are also in excellent agreement with available theoretical calculations based on an electron–gas model. Decomposition of the atom–molecule potentials into constituent atom–atom potentials shows that such a representation can be utilized with fair accuracy but that a definite discrepancy exists.

Scattering of fast potassium ions by small molecules

Measurements have been made of the effective total cross sections for the scattering of potassium ions with energies between 100 and 2350 eV by room temperature O2, N2, CO, NO, CO2, and N2O. The repulsive interaction potentials were deduced from the energy dependence of the cross sections using both the inverse power and exponential representations of the potential function. The results appear to be self‐consistent, indicating no measurable difference between the potentials for K+ interacting with O2, N2, NO, or CO, or between the potentials for K+ interacting with CO2 or N2O. Where it is possible to compare with other work, significant differences are found, as happened previously in reports of potentials of K+ interacting with several rare gas atoms. The potentials were compared to those determined in this laboratory by scattering argon beams with the same molecules and the potentials for the two isoelectronic systems were found, in all cases studied, to be essentially identical and actually cross in th...

Scattering of high‐velocity neutral particles. XVIII. He– (CH3F, CH2F2, CHF3)

Fast He beams have been scattered by room‐temperature CH3F, CH2F2, and CHF3 to obtain the following average potentials (energy in eV and separation in A): He–CH3F, V (r) =3.86×102/r8.34, 2.00<r<2.47; He–CH2F2, V (r) =3.88×104/r13.33, 2.22<r<2.58; He–CHF3, V (r) =4.06×105/r15.43, 2.33<r<2.63. Where they overlap, these results agree with independent measurements by Fink, King, and Freeman. The peripheral‐force approximation, which assumes that the centers of force in a molecule are located at the nuclei of each atom, has been used to calculate potentials for the above systems from previous measurements on He–CH4 and He–CF4. The calculated potentials are in only fair agreement, being systematically high. Sources of the discrepancies are discussed.

Short-range interactions for SF6 and CF4 with He and Ar from molecular-beam scattering☆

Abstract Short-range interactions of HeSF 6 and ArCF 4 are obtained from measurements of the scattering of He and Ar beams in room-temperature gas. It is suggested that these results, together with the previously-reported resuit for HeCF 4 , can serve as useful tests for calculations based on the electron-gas model.

Scattering of high-velocity He atoms by C/CH3/4 and Si/CH3/4

Fast He beams have been scattered by room‐temperature C(CH3)4 and Si(CH3)4 to obtain average atom–molecule potentials. The results do not correlate in any simple way with previous work on He–CH4 and He–SiH4; in particular, the present systems cannot be represented satisfactorily as clusters of four CH4 molecules. Moreover, the effective He⋅⋅⋅H potentials deduced from the present results are much larger than the effective He⋅⋅⋅H potential deduced from He–CH4 results. Possible interpretations of these results are discussed.