Evidence for two-electron processes in the mutual neutralization of O- with O+ and N+ at Subthermal Collision Energies

We have measured total absolute cross sections for the Mutual Neutralization (MN) of O- with O+/N+. A fine resolution (of about 50 meV) in the kinetic energy spectra of the product neutral atoms allows unique identification of the atomic states participating in the mutual neutralization process. Cross sections and branching ratios have also been calculated down to 1 meV center-of-mass collision energy for these two systems with a multi-channel Landau-Zener model and an asymptotic method for the ionic-covalent coupling matrix elements. The importance of two-electron processes in one-electron transfer is demonstrated by the dominant contribution of a core-excited configuration of the nitrogen atom in N+ + O- collisions. This effect is partially accounted for by introducing configuration mixing in the evaluation of coupling matrix elements.Comment: 5 pages, 4 figure

Absolute energy-resolved measurements of the H-+H→H2+e- associative detachment reaction using a merged-beam apparatus

Using a merged-beam configuration, we have performed absolute measurements for the associative detachment reaction H-+H→H2+e-. Our energy-resolved measurements for this process remove a long-standing discrepancy between theory and experiment for this fundamental reaction. In particular, we find excellent agreement with theoretical results which previously seemed to be ruled out by earlier experiments performed using a flowing afterglow technique

Generation of neutral atomic beams utilizing photodetachment by high power diode laser stacks

We demonstrate the use of high power diode laser stacks to photodetach fast hydrogen and carbon anions and produce ground term neutral atomic beams. We achieve photodetachment efficiencies of $\sim$7.4\% for H$^-$ at a beam energy of 10\,keV and $\sim$3.7\% for C$^-$ at 28\,keV. The diode laser systems used here operate at 975\,nm and 808\,nm, respectively, and provide high continuous power levels of up to 2\,kW, without the need of additional enhancements like optical cavities. The alignment of the beams is straightforward and operation at constant power levels is very stable, while maintenance is minimal. We present a dedicated photodetachment setup that is suitable to efficiently neutralize the majority of stable negative ions in the periodic table

Associative detachment of H− + H → H2 + e−

Using a merged-beams apparatus, we have measured the associative detachment (AD) reaction of H−+H→H2+e− for relative collision energies up to Er≤4.83 eV. These data extend above the 1-eV limit of our earlier results. We have also updated our previous theoretical work to account for AD via the repulsive 2Σg+ H2− potential energy surface and for the effects at Er≥0.76 eV on the experimental results due to the formation of long-lived H2 resonances lying above the H+H separated atoms limit. Merging both experimental data sets, our results are in good agreement with our new theoretical calculations and confirm the prediction that this reaction essentially turns off for Er≳2 eV. Similar behavior has been predicted for the formation of protonium from collisions of antiprotons and hydrogen atoms

Molecular Hydrogen Formation in the Early Universe: New Implications From Laboratory Measurements

We have performed the first energy-resolved measurement of the associative detachment (AD) reaction H- + H → H2 + e-: This reaction is the dominant formation pathway for H2 during the epoch of first star formation in the early universe. Despite being the most fundamental anion-neutral chemical reaction, experiment and theory have failed to converge in both magnitude and energy dependence. The uncertainty in this rate coefficient severely limits our under- standing of the formation of the first stars and protogalaxies

CCE estimation of factor-augmented regression models with more factors than observables

This paper considers estimation of factor-augmented panel data regression models with homogenous slope coefficients. One of the most popular approaches towards this end is the pooled common correlated effects (CCE) estimator of Pesaran (2006). For this estimator to be consistent at the usual sqrt-NT rate, where N and N denote the number of cross-section and time series observations, respectively, the number of factors cannot be larger than the number of observables. This is a problem in the typical application involving only a small number of regressors. The current paper proposes a simple extension to the CCE procedure by which the requirement can be relaxed. The CCE approach is based on taking the cross-section average of the observables as an estimator of the common factors. The idea put forth in the current paper is to consider not only the average but also other cross-section combinations. The asymptotic properties of the resulting combination-augmented CCE (C3E) estimator are provided and verified in small samples using Monte Carlo simulation

Molecular Hydrogen Formation in the Early Universe: New Implications From Laboratory Measurements

We have performed the first energy-resolved measurement of the associative detachment (AD) reaction H- + H → H2 + e-: This reaction is the dominant formation pathway for H2 during the epoch of first star formation in the early universe. Despite being the most fundamental anion-neutral chemical reaction, experiment and theory have failed to converge in both magnitude and energy dependence. The uncertainty in this rate coefficient severely limits our under- standing of the formation of the first stars and protogalaxies

Isotope effect for associative detachment: H(D)−+H(D)→H2(D2)+e

We report experimental and theoretical results for associative detachment (AD) of D−+D→D2+e−. We compare these data to our previously published results for H−+H→H2+e−. The measurements show no significant isotope effect in the total cross section. This is to be contrasted with previously published experimental and theoretical work which has found a significant isotope effect in diatomic systems for partial AD cross sections, i.e., as a function of the rotational and vibrational levels of the final molecule formed. Our work implies that though the rovibrational distribution of flux is different for AD of H− + H and D− + D, the total flux for these two systems is essentially the same when summed over all possible final channels

Vibrational state distribution of 2-Na^+ ions created in ultracold collisions

The vibrational distribution P(v) of 2-Na^+ ions created in ultracold collisions in a magneto-optical trap has been deter- mined. Only two vibrational states with v = 2 and 3 are popu- lated and we find P(2)=0.29±0.02 and P(3)=0.71±0.02. The results provide conclusive evidence that the ionization mech- anism is photo-associative autoionization,and not photo- associative photoionization and will form a fundamental test for the theoretical description of the process

Hemihepatectomy and Replacement of The Afferent Hepatic Blood Supply in The Dog

Hemihepatectomy along with portal vein or hepatic artery replacement in dogs was well tolerated, but combined with replacement of both vessels it was lethal because of outflow block and shock. Total liver blood flow should be kept as high as possible during such procedures in man