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.