ABSTRACT A cryogenically cooled linear electrostatic ion beam trap for use in photoelectron-photo... more ABSTRACT A cryogenically cooled linear electrostatic ion beam trap for use in photoelectron-photofragment coincidence (PPC) spectroscopy is described. Using this instrument, anions created in cold, low-duty-cycle sources can be stored for many seconds in a ~20 K environment to cool radiatively, removing energetic uncertainties due to vibrationally excited precursor anions. This apparatus maintains a well-collimated beam necessary for high-resolution fragment imaging and the high experimental duty cycle needed for coincidence experiments. Ion oscillation is bunched and phase-locked to a modelocked laser, ensuring temporal overlap between ion bunches and laser pulses and that ions are intersected by the laser only when travelling in one direction. An electron detector is housed in the field-free center of the trap, allowing PPC experiments to be carried out on ions while they are stored and permitting efficient detection of 3-dimensional electron and neutral recoil trajectories. The effects of trapping parameters on the center-of-mass trajectories in the laser-ion interaction region are explored to optimize neutral particle resolution, and the impact of bunching on ion oscillation is established. Finally, an initial demonstration of radiative cooling is presented.
ABSTRACT Dissociation dynamics of the deuterated formyloxyl radical, DCO2, were studied by photoe... more ABSTRACT Dissociation dynamics of the deuterated formyloxyl radical, DCO2, were studied by photoelectron–photofragment coincidence spectroscopy of DCO2-. Photodetachment at 4.27 eV accesses the three lowest-lying electronic states (2A1, 2B2, and 2A2) of DCO2, leading to vibrational excitation dominated by the 2A1 state O−C−O bending mode. Predissociation leads to bending excitation in the CO2 products as observed in the product translational energy distribution. Gating the coincidence spectra by electron kinetic energy for each predissociated vibrational mode in the radical provides a direct measure of the CO2 bending vibration (ν2) product state distribution, revealing substantially more excitation than ab initio quantum-dynamics calculations predict.
The ethoxy radical is an important species in combustion chemistry; however, considerable debate ... more The ethoxy radical is an important species in combustion chemistry; however, considerable debate regarding the fragmentation pathways exists. In order to examine the stability and dissociation dynamics of the ethoxy radical in the two lowest electronic states, dissociative photodetachment experiments at 3.20 eV were carried out on the ethoxide anion, CH3CH2O(-), and its per-deuterated isotopologue. Production of excited radicals by photodetachment of the alkoxide anion was found to lead to only CH3 + H2CO products, with no indication of the energetically allowed H-loss channel, H + CH3CHO. Ab initio calculations for the anionic and neutral surfaces, including relevant isomerization and dissociation barriers, were carried out using the CBS-QB3 method to aid in interpretation of the data. The energetics observed in the photoelectron-photofragment coincidence spectra indicate that the calculated barrier (0.70 eV) for the process CH3CH2O → CH3 + H2CO and the stability of the CH3CH2O radical relative to those products are upper limits.
The study of gas-phase reaction dynamics has advanced to a point where four-atom reactions are th... more The study of gas-phase reaction dynamics has advanced to a point where four-atom reactions are the proving ground for detailed comparisons between experiment and theory. Here, a combined experimental and theoretical study of the dissociation dynamics of the tetra-atomic FH2O system is presented, providing snapshots of the F + H2O → HF + OH reaction. Photoelectron-photofragment coincidence measurements of the dissociative photodetachment (DPD) of the F(-)(H2O) anion revealed various dissociation pathways along different electronic states. A distinct photoelectron spectrum of stable FH-OH complexes was also measured and attributed to long-lived Feshbach resonances. Comparison to full-dimensional quantum calculations confirms the sensitivity of the DPD measurements to the subtle dynamics on the low-lying FH2O potential energy surfaces over a wide range of nuclear configurations and energies.
Photoionization mass spectrometry using tunable vacuum-ultraviolet synchrotron radiation is appli... more Photoionization mass spectrometry using tunable vacuum-ultraviolet synchrotron radiation is applied to the study of C3H2 sampled from a rich cyclopentene flame. The photoionization efficiency has been measured between 8.5 eV and 11.0 eV. FranckCondon factors for ...
ABSTRACT A cryogenically cooled linear electrostatic ion beam trap for use in photoelectron-photo... more ABSTRACT A cryogenically cooled linear electrostatic ion beam trap for use in photoelectron-photofragment coincidence (PPC) spectroscopy is described. Using this instrument, anions created in cold, low-duty-cycle sources can be stored for many seconds in a ~20 K environment to cool radiatively, removing energetic uncertainties due to vibrationally excited precursor anions. This apparatus maintains a well-collimated beam necessary for high-resolution fragment imaging and the high experimental duty cycle needed for coincidence experiments. Ion oscillation is bunched and phase-locked to a modelocked laser, ensuring temporal overlap between ion bunches and laser pulses and that ions are intersected by the laser only when travelling in one direction. An electron detector is housed in the field-free center of the trap, allowing PPC experiments to be carried out on ions while they are stored and permitting efficient detection of 3-dimensional electron and neutral recoil trajectories. The effects of trapping parameters on the center-of-mass trajectories in the laser-ion interaction region are explored to optimize neutral particle resolution, and the impact of bunching on ion oscillation is established. Finally, an initial demonstration of radiative cooling is presented.
ABSTRACT Dissociation dynamics of the deuterated formyloxyl radical, DCO2, were studied by photoe... more ABSTRACT Dissociation dynamics of the deuterated formyloxyl radical, DCO2, were studied by photoelectron–photofragment coincidence spectroscopy of DCO2-. Photodetachment at 4.27 eV accesses the three lowest-lying electronic states (2A1, 2B2, and 2A2) of DCO2, leading to vibrational excitation dominated by the 2A1 state O−C−O bending mode. Predissociation leads to bending excitation in the CO2 products as observed in the product translational energy distribution. Gating the coincidence spectra by electron kinetic energy for each predissociated vibrational mode in the radical provides a direct measure of the CO2 bending vibration (ν2) product state distribution, revealing substantially more excitation than ab initio quantum-dynamics calculations predict.
The ethoxy radical is an important species in combustion chemistry; however, considerable debate ... more The ethoxy radical is an important species in combustion chemistry; however, considerable debate regarding the fragmentation pathways exists. In order to examine the stability and dissociation dynamics of the ethoxy radical in the two lowest electronic states, dissociative photodetachment experiments at 3.20 eV were carried out on the ethoxide anion, CH3CH2O(-), and its per-deuterated isotopologue. Production of excited radicals by photodetachment of the alkoxide anion was found to lead to only CH3 + H2CO products, with no indication of the energetically allowed H-loss channel, H + CH3CHO. Ab initio calculations for the anionic and neutral surfaces, including relevant isomerization and dissociation barriers, were carried out using the CBS-QB3 method to aid in interpretation of the data. The energetics observed in the photoelectron-photofragment coincidence spectra indicate that the calculated barrier (0.70 eV) for the process CH3CH2O → CH3 + H2CO and the stability of the CH3CH2O radical relative to those products are upper limits.
The study of gas-phase reaction dynamics has advanced to a point where four-atom reactions are th... more The study of gas-phase reaction dynamics has advanced to a point where four-atom reactions are the proving ground for detailed comparisons between experiment and theory. Here, a combined experimental and theoretical study of the dissociation dynamics of the tetra-atomic FH2O system is presented, providing snapshots of the F + H2O → HF + OH reaction. Photoelectron-photofragment coincidence measurements of the dissociative photodetachment (DPD) of the F(-)(H2O) anion revealed various dissociation pathways along different electronic states. A distinct photoelectron spectrum of stable FH-OH complexes was also measured and attributed to long-lived Feshbach resonances. Comparison to full-dimensional quantum calculations confirms the sensitivity of the DPD measurements to the subtle dynamics on the low-lying FH2O potential energy surfaces over a wide range of nuclear configurations and energies.
Photoionization mass spectrometry using tunable vacuum-ultraviolet synchrotron radiation is appli... more Photoionization mass spectrometry using tunable vacuum-ultraviolet synchrotron radiation is applied to the study of C3H2 sampled from a rich cyclopentene flame. The photoionization efficiency has been measured between 8.5 eV and 11.0 eV. FranckCondon factors for ...
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Papers by Amelia Ray