Yozaburo Kaneko

Formation of Helium Cluster Ions 4Hen+ (n≤15) in a Liquid Helium Cooled Drift Tube

Helium cluster ions 4 He n + (2≤ n ≤15) have been formed in a drift tube. Information about binding energy, Δ E n = E n - E n -1 , has been obtained. The binding energy drastically decreases at n =4, then gradually decreases with increasing n . Steplike changes have also been observed between n =10 and 11 and n =14 and 15, which indicates that the cluster sizes n =10 and 14 are magic numbers. Geometrical structures of He 10 + and He 14 + are discussed.

Helium cluster ions RgHe x + (Rg=Ne, Ar and Kr,x≦14) formed in a drift tube cooled by liquid helium

Rare gas ions Ne+, Ar+ and Kr+ are injected into a drift tube which is filled with helium gas and cooled by liquid helium. Helium cluster ions RgHex+ (Rg=Ne, Ar and Kr,x≦14) are observed as products. Information regarding the stability of RgHex+ is obtained from drift field dependence of the size distribution of the clusters, and magic numbers are determined. The magic numbers arex=11 and 13 for NeHex+ andx=12 for ArHex+ and KrHex+. NeHex+, Ar+ and Kr+ are proposed as the core ions for NeHe13+, ArHe12+ and KrHe12+, respectively.

Low Energy Ion-Neutral Reactions. I. 22Ne++20Ne, and Ar++N2

A series of experiments has been performed using drift tube technique, in which both the primary and secondary ions are mass identified. Design of the apparatus is described briefly. Drift velocities of ions in the drift tube are measured with gate pulse technique. Cross sections of reactions 22 Ne + + 20 Ne→ 22 Ne+ 20 Ne + and Ar + +N 2 →Ar+N 2 + are determined as functions of mean energies of the ions in the range from 0.04 to 4 eV. Cross section of the former reaction decreases from 5.2±0.2×10 -15 cm 2 at 0.045 eV to 3.7±0.2×10 -15 cm 2 at 2.5 eV. Comparisons of measured cross section with the theory of Rapp-Francis and the previous experiments show that the technique and apparatus used are quite reliable. Cross section of the latter reaction increases from 3.0±0.3×10 -16 cm 2 at 0.43 eV to 2.2±0.2×10 -15 cm 2 at 4.4 eV, and it does not agree with the previous experiments using beam technique at higher energy.

Vibrational Excitation of CO, CO2 and N2O by Li+ Impact in the Energy Range from 70 eV to 1500 eV

Vibrational excitation of CO, CO 2 and N 2 O by Li + impact was studied with an ion energy-loss spectrometer. The excitation takes place in strongly forward scattering above 400 eV, and absolute total cross sections of excitation are obtained easily. For CO, the cross sections of 0→1 and 0→2 excitation are obtained. For CO 2 , the cross sections for the excitation of (010), (020), (001) and (011) levels are determined. The excitation of the symmetric stretching mode (100) is not observed. For N 2 O, the excitation cross sections of (100), (010), (001), (002) and (101) levels are obtained. The experimental results are compared with the first Born approximation, and a possibility of determining the infrared intensities is discussed.

Low Energy Ion-Neutral Reactions. V. O2++NO, N2++NO, CO++NO, N2++O2, CO2++O2, CO++O2 and N2++CO

Asymmetric charge transfer reactions between molecular ions and molecules; O 2 + –NO, N 2 + –NO, CO + –NO, N 2 + –O 2 , CO 2 + –O 2 , CO + –O 2 and N 2 + –CO were studied by an injected-ion drift tube technique in the energy range from 0.04 eV to 3 eV. For the reaction in the system O 2 + –NO, the processes O 2 + (X 2 \(\varPi_{\text{g}}\))+NO→O 2 +NO + and O 2 + (\(a^{4}\varPi_{\text{u}}\))+NO→O 2 +NO + were distinguished and each cross section was determined separately.

Landau-Zener model calculations of one-electron capture from He atoms by highly stripped ions at low energies

Cross sections for single electron capture from He atom by highly stripped, C q + , N q + , O q + , F q + , Ne q + ( q =4–9) and Kr q + ( q =10–25) ions have been calculated using the multichannel Landau-Zener model. The collision energy is 600 eV/amu except for Kr q + , whose energy is q ×1 keV. The selective electron capture into a single or at most two n -shells is predicted for the cases of q ≤9. The n -distributions obtained by the present calculation are quite consistent with our earlier observation and the total cross sections agree reasonably well with the measured data in spite of the simple model. In the case of Kr q + , where q is larger than 10, more and more shells can be populated and the total cross sections increase monotonically with the increase of q .

Mobilities of He+, Ne+, Ar+, and Kr+ in He gas at 4.35 K

Mobilities of He+, Ne+, Ar+, and Kr+ have been measured in He gas at 4.35 K. An injected‐ion drift tube which can be cooled by liquid helium was used. It has a Wien filter on the ion injection line and a quadrupole mass filter on the detection line so that mass identification is explicitly made. Ions are injected into the drift tube with 20 eV, and it is assured that the thermalization of ions is completed well before reaching the gate for mobility measurement. The correction for thermal transpiration in the pressure measurement was made by Takaishi–Sensui’s empirical formula. The reduced mobility K was measured against E/N, where E is the electric field strength and N is the gas number density. Then the E/N was converted to the effective temperature Teff by Wannier’s formula. The K(Teff) obtained are compared with the previous experimental and theoretical results, some of which are given in K0(Tg), where K0 is the zero field mobility and Tg is the gas temperature. The agreement between the present result...

Fine-Structure Transitions in Ar+(2Pj)+Ar(1S0) Collisions in the Energy Range 60 eV–1500 eV

Direct fine-structure transitions, j=3/2 →1/2 and j=1/2 →3/2, were first observed with an ion energy-loss spectrometer at near 0°. The ions were produced with an electron-impact ion source. The peak heights corresponding to both transitions were almost the same over the energy range studied. The ratio of the 3/2 to 1/2 states in the primary ions was determined to be in statistical ratio, 2:1, assuming detailed balance for the transitions. Partial excitation cross-sections for the forward scattering within the angle ±0.45° were evaluated from the spectra obtained.

The mobility of N2+ and CO+ in helium gas at 4.35 K

The ion mobilities of N2+ and CO+ in He have been measured using a liquid-helium-cooled, selected ion drift tube at 4.35 K. Mobility reaches a maximum at an effective temperature of between 400 K and 600 K, where it is in reasonable agreement with the room temperature measurements of other experimenters. Below 100 K there is a region in which the mobilities are constant, N2+ close to the polarization limit and CO+ somewhat lower, possibly due to the occurrence of collisionally induced, rotational excitation. At very low effective temperature though, below 10 K, the mobilities decrease sharply, below the polarization limit. This may be further evidence for the existence of orbiting resonance such as that suggested previously by Kojima et al. for He+ in He.

Absolute Measurement of Total Ionization Cross Section of Mg by Electron Impact

Total ionization cross section of Mg by electron impact has been measured absolutely by the crossed beam technique. Intensity of neutral Mg beam is determined by the deposition method. Mg atoms deposited onto a beam collector are quantitatively analyzed by atomic absorption spectrophotometry. The absolute cross sections at 22.4 eV, 106 eV, 492 eV and 1000 eV are determined to be 9.1, 3.9, 1.7 and 1.0×10 -16 cm 2 , respectively. Systematic errors are estimated to be within -15% and +8%. Relative cross section is obtained as a function of electron energy from the threshold to 1130 eV. The results are compared with some experimental results and theoretical calculations by other workers.