Studies of atmospheric molecules by multiphoton spectroscopy

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Carbon dioxide presents a great challenge to spectroscopy because of its propensity toward dissociation in all of its excited states. Multiphoton ionization spectroscopy is usually not applicable to the study of dissociating molecules because the dissociation competes effectively with ionization, resulting in no signal. We reasoned, however, that with high enough laser fluence, ionization could compete with dissociation in the longer lived states, exposing them for study from the continuous spectral background resulting from rapidly dissociating states. We describe the various spectroscopic and photophysical effects found through the multiphoton ionization and multiphoton photoelectron spectra. A recently developed variant of threshold ... continued below

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Pages: (24 p)

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Johnson, P.M. October 1, 1991.

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Description

Carbon dioxide presents a great challenge to spectroscopy because of its propensity toward dissociation in all of its excited states. Multiphoton ionization spectroscopy is usually not applicable to the study of dissociating molecules because the dissociation competes effectively with ionization, resulting in no signal. We reasoned, however, that with high enough laser fluence, ionization could compete with dissociation in the longer lived states, exposing them for study from the continuous spectral background resulting from rapidly dissociating states. We describe the various spectroscopic and photophysical effects found through the multiphoton ionization and multiphoton photoelectron spectra. A recently developed variant of threshold ionization spectroscopy, usually called ZEKE, has shown a great deal of usefulness in providing the same information as traditional photoelectron spectroscopy but with higher resolution and much better signal-to-noise when using standard laboratory lasers. Threshold ionization techniques locate the states of an ion by scanning a light source across the ionization continuum of a neutral and somehow detecting when electrons are produced with no kinetic energy. We chose to develop our capabilities in threshold ionization spectroscopy using aromatic molecules because of their importance and because their electronic structure allows a pump-probe type of excitation scheme which avoids the use of vacuum ultraviolet laser beams. Among aromatics, the azines are noted for their small S{sub 1}-T{sub 1} energy gap which give them unique and interesting photophysical properties. We have continued our work on the multiphoton spectrum of metastable nitrogen produced by an electric discharge in supersonic beam. We have been able to assign more of the lines and simulated their rotational structure but many peaks remain unassigned.

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Pages: (24 p)

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OSTI; NTIS; GPO Dep.

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  • Other: DE92012668
  • Report No.: DOE/ER/13590-10
  • Grant Number: FG02-86ER13590
  • DOI: 10.2172/5394803 | External Link
  • Office of Scientific & Technical Information Report Number: 5394803
  • Archival Resource Key: ark:/67531/metadc1073533

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  • October 1, 1991

Added to The UNT Digital Library

  • Feb. 4, 2018, 10:51 a.m.

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  • March 1, 2018, 8:11 p.m.

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Johnson, P.M. Studies of atmospheric molecules by multiphoton spectroscopy, report, October 1, 1991; United States. (digital.library.unt.edu/ark:/67531/metadc1073533/: accessed April 26, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.