Multi-body dissociative photodetachment dynamics of small molecular and cluster anions.

摘要

Photoelectron-photofragment coincidence (PPC) spectroscopy was employed to study the dissociation dynamics of a number of small anionic systems after photodetachment. Photodetachment of anionic precursors often produces a neutral near the reaction transition state, providing a method of probing transition state dynamics. Coincident detection and energy analysis of the photoelectron and all photofragments from two-, three-, and four-body dissociations provides insight into energy partitioning among translational and internal degrees of freedom and the dynamics of multi-body dissociation. Monte Carlo simulations were also employed to elucidate detailed mechanisms of three-body dissociations.; The OH + CO → H + CO2 potential surface was explored through DPD of the molecular anions HOCO- and H-CO 2-. DPD of HOCO- resulted in production of OH + CO e- and H + CO2 + e- as well as stable HOCO + e-. Only the H + CO2 + e- channel was accessed through DPD of H-CO2-. The S2O 2- molecular anion also showed evidence of DPD to multiple product channels.; DPD of small clusters were also studied, including O-(H 2O)2, OH-(H2O)2, (SO2)3-, O8- , and (NO2)n- (n = 2--5). The studies of O-(H2O)2 and OH -(H2O)2 probed the three-body dissociation dynamics, and yielded the first experimental determination of the second hydration energy of O-, 0.71 +/- 0.08 eV. The three-body dissociation dynamics of (SO2)3 showed evidence of a dimer core, consistent with previous work. DPD of (NO2)n - clusters showed evidence of formation of the N2O 4- molecular anion in clusters with n ≥ 2. The first kinematically complete investigation of four-body dissociation dynamics was reported for DPD of O8-. This demonstration of a five particle (4O2 + e-) coincidence experiment represents the highest-order coincidence measurement ever for chemical applications. The dissociation dynamics showed evidence for an O4 - core, as found in the O6- system, with two asymmetrically solvating O2 molecules.; The three-body dissociation dynamics of many systems were also studied through Monte Carlo simulations. These simulations reproduce the data with a simple kinematic model, and provide estimates of intermediate lifetimes in two-step dissociations. For O3(D2O) and O6, the simulations were most consistent with very short intermediate lifetimes while the N2O4-NO2 intermediate resulting from DPD of N2O4-(NO2) 2 appears to live for longer than its rotational period.