Ryan S. DaBell

Electronic structure of the 4d transition metal carbides: Dispersed fluorescence spectroscopy of MoC, RuC, and PdC

Dispersed fluorescence studies of the diatomic molecules MoC, RuC, and PdC are reported. New states identified in MoC and RuC are the […]2δ112σ1, 3,1Δ2 states and the […]2δ312σ1, 1Δ2 state, respectively. Five states are observed by dispersed fluorescence in PdC. The ground state is found to be […]2δ412σ2, 1Σ+, with the […]2δ412σ16π1, 3ΠΩ manifold of states lying about 2500 cm−1 above the ground state. The [17.9]Ω=1 state of PdC is also identified as […]2δ412σ113σ1, 3Σ+(Ω=1), corroborating recent results of resonant two photon ionization spectroscopy studies. The spin-orbit interactions of these molecules are analyzed to deduce the composition of the molecular orbitals, and comparisons are made to ab initio theory when possible. An examination of the trends in bond energy, bond length, and vibrational frequency among the 4d transition metal carbides is also provided.

Resonant two-photon ionization spectroscopy of jet-cooled RuC

A resonant two-photon ionization study of the jet-cooled RuC molecule has identified the ground state as a 1Σ+ state arising from the 10σ211σ25π42δ4 configuration. The 3Δi state arising from the 10σ211σ25π42δ312σ1 configuration lies very low in energy, with the 3Δ3 and 3Δ2 components lying only 76 and 850 cm−1 above the ground state, respectively. Transitions from the X 1Σ+, 3Δ3, and 3Δ2 states to the 3Π2, 3Π1, 3Φ3, 3Φ4, 1Φ3, and 1Π1 states arising from the 10σ211σ25π42δ36π1 configuration have been observed in the 12 700–18 100 cm−1 range, allowing all of these states to be placed on a common energy scale. The bond length increases as the molecule is electronically excited, from r0=1.608 A in the 2δ4, X 1Σ+ state, to 1.635 A in the 2δ312σ1, 3Δ state, to 1.66 A in the 2δ36π1, 3Π and 3Φ states, to 1.667 A in the 2δ36π1, 1Φ and 1.678 A in the 2δ36π1, 1Π state. A related decrease in vibrational frequency with electronic excitation is also observed. Hyperfine splitting is observed in the 2δ312σ1, 3Δ3 state for...

Trends in microwave spectroscopy for the detection of chemical agents

Recent developments in microwave spectroscopy have encouraged researchers to develop this technique for analytical applications such as environmental monitoring, industrial process control, and homeland defense. This paper presents a general overview of microwave spectroscopy with a focus on aspects relevant for detecting chemical warfare agents (CWAs) and their surrogates. In particular, the high spectral resolution of microwave methods provides exceptional selectivity which is critical for detecting and identifying CWAs given the complex environments and numerous interferents that may obscure measurements by instruments with poor specificity. Ongoing efforts to develop a microwave spectral database of CWAs and improve the quantitative capabilities of Fourier transform microwave spectrometers are discussed. Additionally, future improvements to achieve a field-deployable sensor are presented.

Evaluation of Fourier-transform microwave spectroscopy as a tool for quantitative analysis: signal stability considerations

There is a continuing need for improved analytical techniques to measure the concentration of trace gases for monitoring hazardous air pollutants, industrial emissions, chemical-warfare agent release, etc. Methods of analysis that can conclusively identify several analytes in a mixture are particularly desired. Towards this end, the use of Fourier-transform microwave (FTMW) spectroscopy as a quantitative analytical technique has been proposed. The high spectral resolution of FTMW provides a quick and unambiguous method for identifying multiple analytes in the gas phase. A small-scale FTMW spectrometer has recently been constructed for use in quantitative analysis. Prior to the present investigation, however, the use of this spectrometer in quantitative work has not been rigorously evaluated. This work summarizes efforts to identify and categorize sources of signal instability in the FTMW spectrometer. Methods employed to minimize these effects will also be discussed.