ALBERT

Notes: Magnetic Fe-Bi multilayers have been, for the first time, synthesized by using electron-beam evaporation at 140 K. The relationships between film structure and magnetic properties were investigated by means of measurements of magnetization, x-ray diffraction, electron diffraction, and Mössbauer spectra. Films are ferromagnetic or paramagnetism, depending on Fe layer thickness, tFe. Films with tFe of about 1 nm exhibit perpendicular magnetic anisotropy while these with the thicker tFe have in-plane magnetism. Temperature dependence of magnetization in the Fe-Bi multilayers was also studied in the temperature range of 77–600 K.

Notes: A detailed three-dimensional quantum mechanical study of the (Ar+H2)+ system along the energy range 0.4 eV≤Etot≤1.65 eV is presented. The main difference between this new treatment and the previously published one [J. Chem. Phys. 87, 465 (1987)] is the employment of a new version of the reactive infinite-order sudden approximation (IOSA), which is based on the ordinary inelastic IOSA carried out for an optical potential. In the numerical treatment we include three surfaces (only two were included in the previous treatment), one which correlates with the Ar+H+2 system and two which correlate with the two spin states of Ar+(2Pj); j=3/2,1/2. The results are compared with both trajectory-surface-hopping calculations and with experiments. In most cases, very good agreement is obtained.

Notes: Total state-selected and state-to-state absolute cross sections for the reactions Ar+(2P3/2,1/2)+H2(X,v=0)→Ar (1S0)+H+2(X˜,v') [reaction (1)], ArH++H [reaction (2)], and H++H+Ar [reaction (3)] have been measured in the center-of-mass collision energy Ec.m. range of 0.24–19.1 eV. Absolute spin–orbit state transition total cross sections (σ3/2→1/2,σ1/2→3/2) for the collisions of Ar+(2P3/2,1/2) with H2 at Ec.m.=1.2–19.1 eV have been obtained.The measured state-selected cross sections for reaction (1) [σ3/2,1/2(H+2)] reveal that at Ec.m.≤5 eV, σ1/2(H+2) is greater than σ3/2(H+2), while the reverse is observed at Ec.m.≥7 eV. The total state-to-state absolute cross sections for reaction (1) (σ3/2,1/2→v') show unambiguously that in the Ec.m. range of 0.16–3.9 eV the dominant product channel formed in the reaction of Ar+(2P1/2)+H2(X,v=0) is H+2(X˜,v'=2)+Ar. These observations support the conclusion that at low Ec.m. the outcome of charge transfer collisions is governed mostly by the close energy resonance effect. However, at sufficiently high Ec.m.(〉6 eV) the charge transfer of Ar+(2P3/2)+H2 is favored compared to that of Ar+(2P1/2)+H2.The relative values measured for X1/2→v'[≡σ1/2→v'/σ1/2 (H+2)] are in good accord with those predicted from calculations using the state-to-state cross sections for the H+2(X˜,v'=0–4)+Ar charge transfer reaction and the relation based on microscopic reversibility. The experimental values for X3/2→v'[≡σ3/2→v'/σ3/2 (H+2)] and those predicted using the microscopic reversibility argument are also in fair agreement. The spin–orbit effect for the cross section of reaction (2) [σ3/2,1/2(ArH+)] is significantly less than that for reaction (1). Both σ3/2(ArH+) and σ1/2(ArH+) decrease rapidly as Ec.m. is increased, and become essentially identical at Ec.m. ≈3.8 eV. The cross sections for reaction (3) observed in the Ec.m. range of 2.5–12 eV are ≤3% of σ3/2,1/2(H+2).The onset for the formation of H+ by reaction (3) is consistent with the thermochemical threshold. The values for σ3/2→1/2 and σ1/2→3/2 observed here are nearly a factor of 2 greater than those measured by the energy loss spectroscopic method. However, the kinetic energy dependencies for σ3/2→1/2 and σ1/2→3/2 are in accord with the previous measurements. Theoretical cross sections for the charge transfer and spin–orbit state transition reactions are calculated at Ec.m.=19.3 eV using the nonreactive infinite-order sudden approximation for comparison with experimental values.

Notes: Total state-selected and state-to-state absolute cross sections for the reactions, H+2(X˜,v'=0–4)+Ar→H2(X,v) +Ar+(2P3/2,1/2) [reaction (I)], ArH++H [reaction (II)], and H++H+Ar [reaction (III)], have been measured in the center-of-mass collision energy (Ec.m.) range of 0.48–100 eV. Experimental state-selected cross sections for reactions (I) and (II) measured at Ec.m.=0.48–0.95 eV are in agreement with those reported previously by Tanaka, Kato, and Koyano [J. Chem. Phys. 75, 4941 (1981)]. The experiment shows that prominent features of the cross sections for reactions (I) and (II) are governed by the close resonance of the H+2(X˜,v'=2)+Ar and H2(X,v=0)+Ar+(2P1/2) vibronic states. At Ec.m.≤3 eV, the vibrational state-selected cross section for the charge transfer reaction (I) is peaked at v'=2.The enhancement of the charge transfer cross section for v'=2 as compared to other v' states of reactant H+2 increases as Ec.m. is decreased. The state-to-state cross sections for reaction (I),measured at Ec.m.≤3 eV, show that the enhancement for the charge transfer cross section for v'=2 is due to the preferential population of Ar+(2P1/2). At Ec.m.=0.48–0.95 eV and v'=2, nearly 80% of the charge transfer product Ar+ ions are formed in the 2P1/2 state. However, at Ec.m.〉5 eV, the intensity for charge transfer product Ar+(2P3/2) is greater than that for Ar+(2P1/2). Contrary to the strong vibrational dependence of the cross section for reaction (I), the cross section for reaction (II) is only weakly dependent on the vibrational state of H+2. At Ec.m.≤3 eV, the cross section for the formation of ArH+ is the lowest for v'=2 compared to other v' states, an observation attributed to the competition of the nearly resonant Ar+(2P1/2)+H2(X,v=0) charge transfer channel. The cross section for reaction (II) decreases with increasing Ec.m..At Ec.m.≥20 eV, the cross sections for the formation of ArH+ become negligible compared to those for Ar+. The appearance energies for the collision-induced dissociation H+2(X˜,v'=0–4) are consistent with the thermochemical threshold for reaction (III). The cross sections the formation of H+ are ≤20% of those for H+2. Theoretical state-to-state cross sections for reaction (I) at Ec.m.=19.3 and 47.6 eV calculated using the nonreactive infinite-order sudden approximation are found to be in fair agreement with experimental results.

Notes: The vibrational state distributions of N+2(X˜,v') ions resulting from the reactions, Ar+(2P3/2)+N2(X˜,v=0)→Ar(1S0) +N+2(X˜,v') [reaction (1)] and Ar+(2P1/2)+N2(X˜,v=0)→Ar(1S0) +N+2(X˜,v') [reaction (2)], over the center-of-mass collisional energy (Ec.m.) range of 0.25–41.2 eV in a crossed ion–neutral beam experiment have been probed by the charge exchange method. The experimental results obtained for reaction (1) are in accord with the predictions of the semiclassical multistate calculation of Spalburg and Gislason that N+2 ions are formed predominantly ((approximately-greater-than)85%) in the v'=1 state and that the production of N+2(X˜,v'=0) becomes more important as Ec.m. is increased. The experiment also supports the theoretical results for reaction (2) at Ec.m.=1.2 and 4.1 eV showing that (approximately-greater-than)80% of N+2 product ions are in the v'=2 state. However, the calculation is found to either over-estimate the populations for N+2(v'〈2) or underestimate the populations for N+2(v'〉2) resulting from reaction (2) at Ec.m.=10.3and 41.2 eV. Absolute spin-orbit-state-selected total cross sections for reactions (1) and (2), σ3/2 and σ1/2, respectively, at the Ec.m. range of 0.25–115.3 eV have also been measured using a tandem photoionization mass spectrometer which is equipped with a radio frequency (RF) octopole ion guide reaction gas cell. The measured values for σ3/2 at Ec.m.=4.1, 10.3, and 41.2 eV and σ1/2 at 41.2 eV are in reasonable agreement with the theoretical cross sections. However, the experimental values for σ3/2 at 1.2 eV and σ1/2 at 1.2, 4.1, and 10.3 eV are approximately a factor of 2 higher than the theoretical predictions. A model analysis, which takes into account possible collision-induced spin-orbit mixings of the reactant Ar+ states in the RF octopole gas cell, shows that the values for σ1/2/σ3/2 and σ1/2 determined using the ion beam–RF octopole gas cell arrangement can be strongly susceptible to gas cell pressure effects whereas the experimental values for σ3/2 are reliable. The values for σ1/2 deduced by multiplying the values for σ3/2 and the ratios σ1/2/σ3/2 determined in the crossed ion–neutral beam experiment are in agreement with the theoretical cross sections. Both σ3/2 and σ1/2 are found to increase as Ec.m. is increased from 41.2 eV. This observation is interpreted as due to the formation of N+2 in the A˜ 2Πu state at high Ec.m. . Combining the measured vibrational state distributions of product N+2(X˜,v') ions and the absolute state-selected total cross sections, absolute state-to-state total cross sections for reactions (1) and (2) at selected Ec.m. are determined.

Notes: Relative vibrational-state-selected total cross sections σv', v'=0–2, for the reaction N+2(X˜,v'=0–2)+Ar(1S0)→N2(X,v +Ar+(2P3/2,1/2) [reaction (1)], over the center-of-mass collisional energy (Ec.m.) range of 1.2–320 eV have been determined using the crossed ion–neutral beam photoionization apparatus. The experimental results at Ec.m.=1.2–40 eV are in agreement with those obtained in previous experimental and theoretical studies, indicating that σ0 is substantially less than σ1 and σ2. As Ec.m. is increased, σ0 becomes comparable to σ1 and σ2 in the Ec.m. range of ∼140–200 eV. At Ec.m.=260 and 320 eV, the cross sections are in the order σ0〉σ1〉σ2. The fractions of Ar+(2P1/2) resulting from reaction (1), Xv'→1/2, v'=0–2, at Ec.m.=4–320 eV have been measured by the charge exchange method. The measurement shows that the Ar+ product ions are predominantly((approximately-greater-than)80%) formed in the 2P3/2 state, an observation qualitatively in accord with the predictions of semiclassical multistate calculations. The predicted values for Xv'→1/2, v'=0–2, at Ec.m.=8, 20, and 40 eV are higher than the experimental values. The values for X0→1/2 at Ec.m.=8–320 eV and X1→1/2 at Ec.m.=4–40 eV are found to increase as Ec.m. is increased, showing the behavior of an endothermic process. The values for X1→1/2 and X2→1/2 remain approximately constant at the the Ec.m. ranges of 40–320 and 8–200 eV, respectively. The measured relative state-to-state cross sections for reaction (1) and the reaction Ar+(2P3/2,1/2)+N2(X,v=0)→Ar(1S0) +N+2(X˜,v') are consistent from the consideration of microscopic reversibility.

Notes: The relative spin-orbit-state-selected total charge transfer cross sections, σ3/2 and σ1/2, for the reactions, Ar+ (2P3/2,1/2)+N2 (X˜ 1∑+g ,v=0) → Ar+N+2 at the center-of-mass collision energy (Ec.m.) range of 0.41–164.7 eV, have been determined using the photoionization and crossed ion–neutral beam methods. The kinetic energy dependences for σ1/2/σ3/2 is found to exhibit a minimum at Ec.m.≈3.3 eV, an observation consistent with the prediction of a recent semiclassical theoretical calculation of Spalburg and Gislason.