A. Weaver

Examination of the 2A’2 and 2E‘ states of NO3 by ultraviolet photoelectron spectroscopy of NO−3

The photoelectron spectrum of the NO−3 anion has been obtained at 266 and at 213 nm. The 266 nm spectrum probes the 2A’2 ground state of NO3. The 213 nm spectrum represents the first observation of the 2E‘ lowest‐lying excited state of NO3. The 2A2 band shows vibrational progressions in the ν1 symmetric stretch and the ν4 degenerate in‐plane bend of NO3. Our analysis of this band indicates that the NO3 ground state has a D3h equilibrium geometry and is vibronically coupled to the 2E’ second excited state via the ν4 mode. We also obtain the electron affinity of NO3, 3.937±0.014 eV, and the heat of formation of NO3 at 298 K, 0.777±0.027 eV (17.9±0.6 kcal/mol). The 2E‘ state of NO3 lies 0.868±0.014 eV above the ground state. The 2E‘ band shows complex and extensive vibrational structure. Several possible assignments of this structure are discussed.

Vibrationally resolved photoelectron spectra of Si−3 and Si−4

Photoelectron spectra of the Si−3 and Si−4 cluster anions have been obtained at 355 and 266 nm. The spectra show transitions to the ground and low‐lying excited electronic states of the neutral clusters. Several of the electronic bands show resolved vibrational structure. The electronic state energies and vibrational frequencies are compared to recent ab initio calculations. The Si−4 spectrum is consistent with the prediction of a planar, symmetric rhombus for the ground state of Si4.

Examination of the Br+HI, Cl+HI, and F+HI hydrogen abstraction reactions by photoelectron spectroscopy of BrHI−, ClHI−, and FHI−

The photoelectron spectra of the ions BrHI−, ClHI−, and FHI−, along with their deuterated counterparts, are presented. These spectra provide information on the transition state region of the potential energy surfaces describing the exothermic neutral reactions X+HI→HX+I(X=Br, Cl, F). Vibrational structure is observed in the BrHI− and ClHI− spectra that corresponds to hydrogen atom motion in the dissociating neutral complex. Transitions to electronically excited potential energy surfaces that correlate to HX+I(2P3/2,2P1/2) products are also observed. A one‐dimensional analysis is used to understand the appearance of each spectrum. The BrHI− spectrum is compared to a two‐dimensional simulation performed using time‐dependent wave packet propagation on a model Br+HI potential energy surface.

Investigation of the F+H2 transition state region via photoelectron spectroscopy of the FH−2 anion

The photoelectron spectrum of the FH−2 anion is reported. The spectrum provides a probe of the transition state region for the F+H2 reaction. The experimental spectrum is compared to the recent simulation by Zhang and Miller which assumes the T5a potential energy surface for the F+H2 reaction. The experimental spectrum is substantially broader. While this may be due to inaccuracies in the T5a surface, the possibility of additional transitions to low‐lying excited electronic surfaces not included in the simulation must also be considered.

Study of hydrogen abstraction reactions by negative ion photoelectron spectroscopy

Photoelectron spectra of the negative ions IHI−, BrHI− and (CH3OH)F− have been recorded at 266 nm and 213 nm. The vibrational structure observed in each spectrum is assigned to the corresponding unstable neutral complex for the bimolecular reaction X+HY→XH+Y. In the case of the centrosymmetric IHI− ion, the neutral complex formed lies near the collinear reaction transition state. For the asymmetric reactions, the geometry of the precursor anion determines whether the reactant or product valley of the reactive surface is probed. The peak positions and widths describe the potential energy surface for the neutral reaction, and in the case of I+HI have been interpreted in terms of a vibrationally adiabatic model.