Rotationally resolved pulsed field ionization photoelectron bands of O{sub 2}{sup +}(X {sup 2}{Pi}{sub 1/2,3/2g},v{sup +}=0{endash}38) in the energy range of 12.05{endash}18.15 eV
- Ames Laboratory, U.S. Department of Energy and Department of Chemistry, Iowa State University, Ames, Iowa 50011 (United States)
- Chemical Science Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720 (United States)
We have obtained rotationally resolved pulsed field ionization photoelectron (PFI-PE) spectra for O{sub 2} in the energy range of 12.05{endash}18.15 eV, covering ionization transitions O{sub 2}{sup +}(X&hthinsp;{sup 2}{Pi}{sub 1/2,3/2g},&hthinsp;v{sup +}=0{endash}38,J{sup +}){l_arrow}O{sub 2}(X&hthinsp;{sup 3}{Sigma}{sub g}{sup {minus}},&hthinsp;v{sup +}=0,N{sup {double_prime}}). While the PFI-PE bands for O{sub 2}{sup +}(X&hthinsp;{sup 2}{Pi}{sub 1/2,3/2g}, v{sup +}=3{endash}5, 9, 11, 12, 22, and 25{endash}38) reported here are the first rotational-resolved photoelectron measurements, the PFI-PE bands for O{sub 2}{sup +}(X&hthinsp;{sup 2}{Pi}{sub 1/2,3/2g},&hthinsp;v{sup +}=25{endash}38) represent the first rotationally resolved spectroscopic data for these states. The simulation of spectra obtained at rotational temperatures of {approx}20 and 220 K allows the unambiguous identification of O{sub 2}{sup +}(X&hthinsp;{sup 2}{Pi}{sub 1/2,3/2g},&hthinsp;v{sup +}{ge}21) PFI-PE bands, the majority of which overlap with prominent PFI-PE bands for O{sub 2}{sup +}(A&hthinsp;{sup 2}{Pi}{sub u},&hthinsp;v{sup +}=0{endash}12) and O{sub 2}{sup +}(a&hthinsp;{sup 4}{Pi}{sub u},&hthinsp;v{sup +}=0{endash}18). Combined with spectroscopic data obtained in the previous emission study and the present PFI-PE experiment, we have obtained accurate Dunham-type expansion coefficients for ionization energies, vibrational constants, rotational constants, and spin{endash}orbit splitting constants covering the O{sub 2}{sup +}(X&hthinsp;{sup 2}{Pi}{sub 1/2,3/2g},&hthinsp;v{sup +}=0{endash}38) states. Significant local intensity enhancements due to near-resonant autoionization were observed in PFI-PE bands for O{sub 2}{sup +}(X&hthinsp;{sup 2}{Pi}{sub 1/2,3/2g},&hthinsp;v{sup +}=0{endash}14). The energy region of these states is known to manifest a high density of very strong autoionizing low-{ital n}-Rydberg states. The observation of a long PFI-PE vibrational progression with a relatively smooth band intensity profile is also in accord with the direct excitation model for the production of highly vibrationally excited O{sub 2}{sup +}(X&hthinsp;{sup 2}{Pi}{sub 1/2,3/2g}) states in the Franck{endash}Condon gap region. Since this experiment was carried out under relatively high rotational temperatures for O{sub 2}, the PFI-PE data reveal higher rotational transitions and numerous local intensity enhancements, which were not observed in previous vacuum ultraviolet laser studies using a cold O{sub 2} molecular beam. The rotational branches found here indicate that photoelectrons are formed predominantly in continuum states with orbital angular momenta l=1,3, and 5. {copyright} {ital 1999 American Institute of Physics.}
- OSTI ID:
- 365875
- Journal Information:
- Journal of Chemical Physics, Vol. 111, Issue 5; Other Information: PBD: Aug 1999
- Country of Publication:
- United States
- Language:
- English
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