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Notes: Absolute state-selected total cross sections σv', v'=0 and 1, for the reaction N+2(X˜,v'=0,1) +Ar(1S0)→N2(X,v)+Ar+(2P3/2,1/2) [reaction (1)] over the center-of-mass collisional energy (Ec.m.) range of 1.2–140 eV have been measured using the photoionization mass spectrometric and radio frequency ion guide methods. These measurements, together with the relative values for σv', v'=0–2, and spin-orbit-state distributions of product Ar+ ions determined using the crossed ion-neutral beam photoionization apparatus, allow the determination of the absolute values for σ2 and partial state-to-state cross sections σv'→J, v'=0–2, for reaction (1). Absolute values for σv', v'=0–2, at Ec.m.=8 and 20 eV are in good agreement with those determined previously by the threshold photoelectron secondary ion coincidence method. Absolute values for σv'→J, v'=0–2, at Ec.m.=8 and 20 eV are also found to be in satisfactory accord with the predictions of the semiclassical multistate calculation which uses the ab initio potential energy surfaces of the [N2+Ar]+ system. Experimental state-to-state cross sections obtained in this study are consistent with those for the reaction Ar+(2P3/2)+N2(X,v=0)→Ar(1S0)+N+2 (X˜,v') from the consideration of microscopic reversibility.

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: We have independently in our two laboratories re-examined the report by Stanton and Sejnowski (Nature, 339, 215 – 218, 1989) that single stimuli to a test pathway in area CA1 of the hippocampal slice, when delivered between short bursts of stimuli to a second, convergent pathway, produce an associative long-term depression (LTD) in the test pathway. While robust associative LTP was observed when stimuli to the two inputs were correlated in time, the anti-correlation procedure failed to induce LTD; rather, a trend towards potentiation was observed. This result was obtained using both submerged and interface chambers, and in two different strains of rat. A transient depression lasting for a few minutes could usually be elicited by strong tetanic stimulation; this depression was not restricted to activated pathways.

Notes: Abstract The mechanism of nucleation and crystal growth of hard gold (Au-Ni) on a gold rotating disc electrode from a proprietary bath (Renovel N) was investigated using linear sweep voltammetry and chronoamperometry. It was shown that two distinct mechanisms in two potential ranges are involved in this process. Experimental current-time transients at more positive potentials were described in terms of three-dimensional progressive nucleation and growth of right-circular cones. Time-independent inhibition of the vertical crystal growth was observed with an increase in negative potential, similar to the soft gold deposition. A modified inhibition model, in which vertical growth rate was assumed to decrease exponentially with time to a constant value, was derived to interpret experimental current-time transients recorded at more negative potentials. The chronoamperometric transients were well described by this model. Potential dependence of initial minima, maxima and final steady-state current was discussed.

Notes: Abstract Deposition of gold on copper from acid gold bath was investigated using electrochemical and microscopic techniques. The growth morphology of both soft and hard gold deposits was characterized using scanning electron microscopy (SEM) and atomic force microscopy (AFM). Analysis of chronoamperometric transients showed that the mechanism of nucleation and growth of hard gold is three-dimensional progressive nucleation and growth of right-circular cones. This was further confirmed by SEM and AFM measurements. The grain size of hard gold deposit was shown to be much smaller than that of soft gold, indicating that nickel in deposit acts as a grain refiner. The mean roughness of hard gold deposit increases with deposition time, and with an increase of negative potential from --0.5 to --0.70V (vs SCE), however, the surface becomes more uniform at --0.80V. Similarly, the maximum height of clusters increases as potential is made more negative between --0.50 and --0.65V, while it decreases steeply at potentials from --0.65 to --0.80V. The inhibition of crystal growth in gold deposition at certain potentials was observed electrochemically and corroborated by microscopic techniques.

Notes: Abstract Electrodeposition of nickel hardened gold was studied from a proprietary bath (Renovel N). Linear sweep voltammetry (LSV), chronoamperometry and chronopotentiometry were employed and Tafel curves determined. LSV studies revealed formation of a current peak connected with the inhibition of the deposition reaction. In the hard gold bath Tafel curves are characterized by two slopes: −0.47 V dec.−1 between −0.5 and −0.8 V and −0.19 V dec.−1 at more negative potentials; in the soft gold bath (without Ni) these slopes are: −0.35 V dec.−1 and −0.15 V dec.−1, respectively. Current efficiency of hard gold plating in galvanostatic conditions was on the average 54–57%, depending more on current density than on the charge passed (thickness of the deposit). No influence of oxygen on the process was found. It was also found, that the bath must be activated before reproducible results are obtained.

Notes: Abstract The initial stages of gold electrodeposition on a gold electrode were studied in a proprietary bath (Renovel N) using linear sweep voltammetry and chronoamperometry. Tafel plots with two different slopes were obtained, indicating that the mechanism for gold deposition depends on potential. An inhibition phenomenon was observed during gold electrocrystallization. Experimental current-time transients were analysed using nonlinear least-squares approximations by various models of nucleation and crystal growth. The electrodeposition mechanism changes from three-dimensional progressive at lower overpotentials to three-dimensional instantaneous at higher overpotentials. Moreover, additional two-dimensional progressive or a secondary three-dimensional progressive processes take place in certain potential ranges. It was shown that the outward growth rate of the substrate's base plane displays a linear Tafel relationship whereas the vertical growth rate of gold crystals decreases at more negative potentials due to an inhibition process.