David J. Leahy

High‐resolution angle‐ and energy‐resolved photoelectron spectroscopy of NO: Partial wave decomposition of the ionization continuum

We report a two‐color high‐resolution energy‐ and angle‐resolved study of the photoelectrons produced in the (1+1’) REMPI of NO via rotational levels of the A 2Σ+ v=0 state. We find markedly different photoelectron angular distributions arising from production of ions in different rotational states (ΔN=0,±1,±2 transitions in the ionization step). We also observe that the ΔN=±2 angular distributions are very sensitive to the intermediate state alignment. A model is put forward in which experimental observables (angle‐ and energy‐resolved photoelectron spectra) are used to determine the attributes (relative amplitudes and phase shifts) of a small number of interfering continuum channels that contribute to the ionization step as well as the fraction of parallel character of the ionization step. Nearly 70% of the ejected photoelectrons are associated with the ΔN=0 ionization transition; the partial wave composition of these electrons is dominated by p character. The less important ΔN=±1 peaks have both s‐ and...

Complete description of two‐photon (1+1’) ionization of NO deduced from rotationally resolved photoelectron angular distributions

Time‐of‐flight photoelectron spectroscopy has been used to record energy‐resolved photoelectron angular distributions (PADs) following (1+1’) resonance‐enhanced multiphoton ionization (REMPI) of NO via the vi=1,Ni=22 rovibrational level of the A 2∑+ state. The PADs corresponding to single rotational states of the resulting molecular ion show a strong dependence on the change in ion core rotation ΔN(≡N+−Ni) and also on the angle between the linear polarization vectors of the two light beams. Broken reflection symmetry [I(θ,φ)≠I(−θ,φ)] is observed when the polarization vectors of the two light beams form an angle of 54.7°. A fit to the PADs provides a complete description of this molecular photoionization, namely, the magnitudes and phases of the radial dipole matrix elements that connect the intermediate state to the ‖lλ〉 photoelectron partial waves (Refs. 1 and 2). This information is then used to predict unobserved quantities, such as ion angular momentum alignment and the full three‐dimensional form of ...

Measurement of circular dichroism in rotationally resolved photoelectron angular distributions following the photoionization of NO A 2Σ

The photoionization process NO A 2Σ+ (v=0, N=22)→NO+ X 1Σ+ (v+=0, N+)+e− is studied with sufficient photoelectron energy resolution that the photoelectron angular distributions (PADs) associated with individual rotational levels N+ of the ion are determined. By ionizing with left and right circularly polarized light and observing the change in the rotationally resolved PADs, we can deduce all dynamical information, including the signs of the relative phase shifts of the photoelectron partial waves. This information constitutes the first complete description of the photoionization of a molecule. We discuss the consistency of our dynamical parameters with the Rydberg series of NO. We present a general formalism for (1+1’) resonance‐enhanced multiphoton ionization (REMPI) PADs for rotationally resolved ion states using linearly polarized light for excitation and elliptically polarized light for ionization. Based on the dynamical parameters determined from our fit, we use this formalism to predict the total s...

Effect of breaking cylindrical symmetry on photoelectron angular distributions resulting from resonance-enhanced two-photon ionization

An expression is derived for the photoelectron angular distribution (PAD) following (1+1’) resonance‐enhanced multiphoton ionization (REMPI) of a molecule with linearly polarized light beams. When the two polarization vectors are parallel, cylindrical symmetry exists, and the PAD depends only on θ, the angle between the linear polarization vector of the ionizing radiation and the electron ejection direction. When the polarization vectors are perpendicular, cylindrical symmetry is broken, and the PAD shows φ and θ dependence. For an arbitrary angle between the two polarization vectors, the angular distribution ceases to have reflection symmetry. This breaking of cylindrical symmetry causes interference effects in the REMPI process that are readily described using a density matrix formalism. As an example, the (1+1’) REMPI of NO via its A 2Σ+ state is considered.

Portal-based knowledge environment for collaborative science.

The Knowledge Environment for Collaborative Science (KnECS) is an open‐source informatics toolkit designed to enable knowledge Grids that interconnect science communities, unique facilities, data, and tools. KnECS features a Web portal with team and data collaboration tools, lightweight federation of data, provenance tracking, and multi‐level support for application integration. We identify the capabilities of KnECS and discuss extensions from the Collaboratory for Multi‐Scale Chemical Sciences (CMCS) which enable diverse combustion science communities to create and share verified, documented data sets and reference data, thereby demonstrating new methods of community interaction and data interoperability required by systems science approaches. Finally, we summarize the challenges we encountered and foresee for knowledge environments. Copyright