Studies of atmospheric molecules by multiphoton spectroscopy

Technical Report · Tue Oct 01 04:00:00 EDT 1991

DOI:https://doi.org/10.2172/5394803· OSTI ID:5394803

Johnson, P M

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.

• Research Organization: State Univ. of New York, Stony Brook, NY (United States). Dept. of Chemistry
• Sponsoring Organization: DOE; USDOE, Washington, DC (United States)
• DOE Contract Number: FG02-86ER13590
• OSTI ID: 5394803
• Report Number(s): DOE/ER/13590-10; ON: DE92012668
• Country of Publication: United States
• Language: English

Related Subjects

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
400500 -- Photochemistry
664400* -- Experimentally Derived Information on Atomic & Molecular Properties-- (1992-)
74 ATOMIC AND MOLECULAR PHYSICS
AZINES
CARBON COMPOUNDS
CARBON DIOXIDE
CARBON OXIDES
CHALCOGENIDES
DISSOCIATION
DOCUMENT TYPES
ELECTRON SPECTROSCOPY
ELEMENTS
ENERGY
ENERGY GAP
ENERGY LEVELS
EXCITED STATES
HETEROCYCLIC COMPOUNDS
IONIZATION
MULTI-PHOTON PROCESSES
NITROGEN
NONMETALS
ORGANIC COMPOUNDS
ORGANIC NITROGEN COMPOUNDS
OXIDES
OXYGEN COMPOUNDS
PHOTOELECTRON SPECTROSCOPY
PHOTOIONIZATION
PROGRESS REPORT
PYRAZINES
ROTATIONAL STATES
RYDBERG STATES
SPECTROSCOPY
THRESHOLD ENERGY