Index of content:
Volume 115, Issue 2, 08 July 2001
115(2001); http://dx.doi.org/10.1063/1.1384008View Description Hide Description
Catalytic ammonia synthesis is believed to proceed via dissociation of and with subsequent stepwise addition reactions from an adsorbed nitrogen atom to The first step, dissociation, has been thoroughly studied. However, little is known about the microscopic details of the stepwise addition reactions. To shed light on these stepwise addition reactions,density functional theory calculations with the generalized gradient approximation are employed to investigate formation on Ru(0001). Transition states and reaction barriers are determined in each elementary step. It is found that the reaction barriers for stepwise addition reactions are rather high, for example, the barrier for NH hydrogenation is calculated to be 1.28 eV, which is comparable with that of dissociation. In addition, one of the stepwise addition reactions on a stepped surface is also considered. The reaction barrier is found to be much higher than that of dissociation on the same stepped surface, which indicates the importance of stepwise addition reactions in ammonia synthesis.
Femtochemistry of mass-selected negative-ion clusters of dioxygen: Charge-transfer and solvation dynamics115(2001); http://dx.doi.org/10.1063/1.1384549View Description Hide Description
Femtosecond,time-resolvedphotoelectron spectroscopy is used to investigate the dissociationdynamics of mass-selected anionic molecular-oxygen clusters. The observed transient photoelectron signal for the clusters shows the production; for and 2, we observe no time-dependence at this wavelength of 800 nm. The observed transients are bi-exponential in form with two distinct time constants, but with clear trends, for all investigated cluster sizes. These striking observations describe the reaction pathways of the solvated core and we elucidate two primary processes: Charge transfer with concomitant nuclear motion, and direct dissociation of the core-ion via electron recombination; the former takes 700–2700 fs, while the latter is on a shorter time scale, 110–420 fs. Both rates decrease differently upon increasing cluster size, indicating the critical role of step-wise solvation.
115(2001); http://dx.doi.org/10.1063/1.1385163View Description Hide Description
We employ Monte Carlo simulations and two versions of integral equation theory to study the potential of mean force between two dilute solutes in a supercritical solvent. The nonlocal integral equation theory is shown to be far superior compared to its homogeneous counterpart. Important differences in the behavior of the potential of mean force between medium and high density solvents are pointed out.