Articles you may be interested inA tunable low-energy photon source for high-resolution angle-resolved photoemission spectroscopy Rev. Sci. Instrum. 83, 113103 (2012); 10.1063/1.4766962High-resolution algorithm for quantitative elemental depth profiling by angle-resolved x-ray photoelectron spectroscopy J. Vac. Sci. Technol. A 15, 2122 (1997 10.1116/1.580618 Molecularorbital decomposition of the ionization continuum for a diatomic molecule by angle and energy resolved photoelectron spectroscopy. II. Ionization continuum of NO Molecularorbital decomposition of the ionization continuum for a diatomic molecule by angle and energy resolved photoelectron spectroscopy. I. FormalismWe 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 2~+ v = 0 state. We find markedly different photoelectron angular distributions arising from production of ions in different rotational states (AN = 0, ± 1, ± 2 transitions in the ionization step). We also observe that the AN = ± 2 angular distributions are very sensitive to the intermediate state alignment. A model is put forward in which experimental observables (angle-and energyresolved 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 AN = 0 ionization transition; the partial wave composition of these electrons is dominated by p character. The less important AN = ± 1 peaks have both s-and d-wave character. The AN = ± 2 photoelectron peaks exhibit far more /-wave than p-wave character because destructive interference nearly removes the p-wave contribution to the angular distribution. The partial wave decomposition is used to predict angular distributions resulting from excitation of the intermediate state by different rotational branch transitions; these predictions are in excellent agreement with the measured distributions.= 2(n + m).10 Finally, it is worth emphasizing that the REMPI process has greatly expanded the number of molecular systems whose photoionization dynamics can be conveniently probed because of the ability to use more than a single photon to reach the ionization continuum.Recently, several experimental techniques have emerged as the techniques of choice for REMPI-PES. The 2216 J.
A tunable, high-intensity picosecond-dye-laser system has been employed with electron energy analysis to investigate the dynamics of (3+ 1) resonance-enhanced multiphoton ionization via various vibrational levels of the B 'X"and C 'Il"electronic states in H2. At the intensities studied [(0.2 -6) X 10" W/cm ], we find evidence for production of molecular ions in various vibrational levels; at the lower intensities the population distribution of final vibrational states varies with wavelength in a manner consistent with resonant enhancement at the three-photon level, followed by ionization into a vibrational level of H2+ roughly predictable by a Franck-Condon analysis of ionization out of the C state. At higher intensities, there is a shift to increased population of lower vibrational states of H2+, consistent with an ac Stark shift of the correspondingly lower vibrational levels of the C state into resonance with the three-photon energy of the laser. Clear evidence of direct dissociation of H2 followed by single-photon ionization of the excited H atom is observed as well. Above-threshold ionization of these two processes occurs readily. We also find that dissociative ionization is an increasingly important ionization pathway as the wavelength is increased. Finally, we see evidence of a fourth ionization pathway, which we tentatively assign to photoionization into a transient bound state created by the avoided crossing of the first repulsive electronic state of H2,~2po. ", n), with the single-photon-dressed ground state of Hz+, isos, n +1).
The development of an optical sensor for basic oxygen furnace (BOF) off-gas composition and temperature in this Advanced Process Control project has seen a laboratory spectroscopic method evolve into a pre-commercialization prototype sensor system. The sensor simultaneously detects an infrared tunable diode laser (TDL) beam transmitted through the process off-gas directly above the furnace mouth, and the infrared greybody emission from the particulate-laden off-gas stream. Following developmental laboratory and field-testing, the sensor prototype was successfully tested in four long-term field trials at Bethlehem Steel's Sparrows Point plant in Baltimore, MD. The resulting optical data were analyzed and reveal correlations with four important process variables: (1) bath turndown temperature; (2) carbon monoxide postcombustion control; (3) bath carbon concentration; and (4) furnace slopping behavior. The optical sensor measurement of the off-gas temperature is modestly correlated with bath turndown temperature (R2 = 0.30). A detailed regression analysis of over 200 heats suggests that a dynamic control level of f 25 O F can be attained with a stand-alone laser-based optical sensor. The ability to track off-gas temperatures to control post-combustion lance practice is also demonstrated, and may be of great use in optimizing post-combustion efficiency in electric furnace steelmaking operations. In addition to the laser-based absorption spectroscopy data collected by this sensor, a concurrent signal generated by greybody emission from the particle-laden off-as was collected variable with final bath turndown carbon concentration. Extended field trials in 1998 and early 1999 show a response range from below 0.03% to at least 0.15% carbon concentration with a precision o f f 0.007%. Finally, a strong correlation was also observed between prolonged drops in the off-gas emission signal and furnace slopping events. A simple computer algorithm was written that successfully predicts furnace slopping for 90% of the heats observed; over 80% are predicted with at least a 30-second warning prior to the initial slopping events. and analyzed. A detailed regression analysis shows an excellent correlation (R F = 0.81) of a single
The thermal hazard posed by a fire to a weapon or other engineered system is a consequence of combined radiation and convection from high-temperature soot and gases. The development of advanced, predictive models of this hazard requires detailed knowledge of the transient chemical structure and soot distributions within real-scale fires. At present, there are no measurements, and hence limited understanding, of transient gaseous species generation and transport in large, fully turbulent fires. As part of a Laboratory Directed Research and Development (LDRD) project to develop such an experimental capability, near-infrared tunable diode laser absorption spectroscopy (TDLAS) has been identified as the most promising diagnostic technique for making these measurements. In order to develop this capability, significant efforts were applied to choosing optimal species and transitions for detection, to developing an effective multiplexing strategy for several lasers undergoing wavelength modulation spectroscopy with fast laser ramp scans, to developing a methodology for multipassing the TDL beams across a small probe volume, and finally, to designing a water-cooled, fiber-coupled probe for performing these measurements locally within large pool fires. All of these challenges were surmounted during the course of this project, and in the end a preliminary, unique dataset of combined water vapor, acetylene, and soot concentrations was obtained from a 1-m diameter JP-8 pool fire.
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