Photoion--photoelectron coincidence study of Ar/sub n/ (n = 2--4)

Journal Article · Wed Mar 15 04:00:00 EST 1989 · J. Chem. Phys.; (United States)

OSTI ID:6549737

Norwood, K; Guo, J; Ng, C Y

Photoion--photoelectron coincidence (PIPECO) spectra for Ar/sup +//sub n/ (n = 2--4) in the wavelength region of 750--875 A have been measured at different nozzle stagnation pressures. The ionization energies (IE) for the ground Ar/sup +//sub 2/(I(1/2)/sub u/) and Ar/sup +//sub 3/(I(1/2)/sub u/) states are determined to be 14.518 +- 0.017 eV (854 +- 1 A) and 14.350 +- 0.033 eV (864 +- 2 A), in agreement with the findings of previous photoionization experiments. The IE for Ar/sup +//sub 2/(II(1/2)/sub u/) is found to be approx. <15.83 eV (783 A). The observation of the Ar/sup +//sub 2/(II(1/2)/sub u/) PIPECO band supports the interpretation that Ar/sup +//sub 2/(II(1/2)/sub u/) is metastable with a lifetime longer than 47 ..mu..s, a value in accord with the calculated radiative lifetime of 90.9 ..mu..s for the II(1/2)/sub u/ ..-->..I(1/2)/sub g/ transition. The PIPECO spectrum for Ar/sup +//sub 2/ is dominated by autoionization structure similar to that resolved in the photoionization efficiency spectrum for Ar/sup +//sub 2/, indicating that a significant fraction of electrons produced by these autoionizing states are slow electrons with near-zero kinetic energies. Evidence is found that metastable Ar/sup +//sub 3/ and Ar/sup +//sub 4/ ions formed by photoionization of Ar/sub 3/ and Ar/sub 4/ at energies above the Ar/sup +//sub 2/(I(1/2)/sub u/)+Ar(/sup 1/S/sub 0/) and Ar/sup +//sub 3/(I(1/2)/sub u/)+Ar(/sup 1/S/sub 0/) dissociation limits may live longer than 58 and 66 ..mu..s, respectively. We suggest that the formation of Ar/sup +//sub 3/ in metastable electronic states may be responsible for the long dissociation lifetimes of Ar/sup +//sub 3/ observed in this experiment.

• Research Organization: Ames Laboratory, U.S. Department of Energy and Department of Chemistry, Iowa State University, Ames, Iowa 50011
• OSTI ID: 6549737
• Journal Information: J. Chem. Phys.; (United States), Journal Name: J. Chem. Phys.; (United States) Vol. 90:6; ISSN JCPSA
• Country of Publication: United States
• Language: English

Related Subjects

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
400201* -- Chemical &amp; Physicochemical Properties
ADDUCTS
ARGON
ARGON COMPLEXES
COINCIDENCE SPECTROMETRY
COMPLEXES
ELECTRON SPECTROSCOPY
ELEMENTS
FLUIDS
GASES
IONIZATION
IONIZATION POTENTIAL
NONMETALS
PHOTOELECTRON SPECTROSCOPY
PHOTOIONIZATION
RARE GASES
SPECTROSCOPY