Rotationally resolved pulsed field ionization photoelectron study of O{sub 2}{sup +}(Bthinsp{sup 2}{Sigma}{sub g}{sup {minus}},{sup 2}{Sigma}{sub u}{sup {minus}};thinspv{sup +}=0{endash}7) at 20.2{endash}21.3 eV
- Ames Laboratory, United States Department of Energy
- Chemical Science Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720 (United States)
We have obtained rotationally resolved pulsed field ionization photoelectron (PFI-PE) spectra of O{sub 2} in the energy range of 20.2{endash}21.3 eV, covering the ionization transitions of O{sub 2}{sup +}(Bthinsp{sup 2}{Sigma}{sub g}{sup {minus}},thinspv{sup +}=0{endash}7,thinspN{sup +}){l_arrow}O{sub 2}(Xthinsp{sup 3}{Sigma}{sub g}{sup {minus}},thinspv{sup {double_prime}}=0,thinspN{sup {double_prime}}). Only the {Delta}N={minus}2, 0, and +2 (or {ital O}, {ital Q}, and {ital S}) rotational branches are observed in the PFI-PE bands for O{sub 2}{sup +}(Bthinsp{sup 2}{Sigma}{sub g}{sup {minus}},thinspv{sup +}=0{endash}7), indicating that the outgoing electron continuum channels with angular momenta l=1 and 3 dominate in the ionization transitions. This experiment allows the determination of accurate spectroscopic constants, such as ionization energy (20.2982{sub 5}{plus_minus}0.0005thinspeV) for the formation of O{sub 2}{sup +}[Bthinsp{sup 2}{Sigma}{sub g}{sup {minus}},thinspv{sup +}=0,thinspN{sup +}=1thinsp(F{sub 2})] from O{sub 2}(Xthinsp{sup 3}{Sigma}{sub g}{sup {minus}},thinspv{sup {double_prime}}=0,thinspN{sup {double_prime}}=1), vibrational constants ({omega}{sub e}{sup +}=1152.91thinspcm{sup {minus}1}, {omega}{sub e}{sup +}{chi}{sub e}{sup +}=20.97thinspcm{sup {minus}1}), and rotational constants (B{sub e}{sup +}=1.255{plus_minus}0.001{sub 5}thinspcm{sup {minus}1}, {alpha}{sub e}{sup +}=0.0241{plus_minus}0.0003{sub 7}thinspcm{sup {minus}1}) for O{sub 2}{sup +}(Bthinsp{sup 2}{Sigma}{sub g}{sup {minus}},thinspv{sup +}). The (nominal) effective lifetimes for high-{ital n} Rydberg states converging to O{sub 2}{sup +}(Bthinsp{sup 2}{Sigma}{sub g}{sup {minus}},thinspv{sup +}=0{endash}6) are measured to be {approx}0.2{endash}0.6 {mu}s, which are significantly shorter than those of {approx}1.9 {mu}s observed for O{sub 2}{sup +}(bthinsp{sup 4}{Sigma}{sub g}{sup {minus}},thinspv{sup +}=0{endash}5). The shorter (nominal) effective lifetimes for high-{ital n} Rydberg states converging to O{sub 2}{sup +}(Bthinsp{sup 2}{Sigma}{sub g}{sup {minus}},thinspv{sup +}=0{endash}6) are attributed to the higher kinetic energy releases (or velocities) of O{sup +}+O fragments resulting from predissociation of the O{sub 2}{sup +}(Bthinsp{sup 2}{Sigma}{sub g}{sup {minus}},thinspv{sup +}=0{endash}6) ion cores. Rotationally resolved PFI-PE measurements also make possible the identification of the weak vibrational progression with the origin at 20.35 eV as associated with transitions to O{sub 2}{sup +}({sup 2}{Sigma}{sub u}{sup {minus}},thinspv{sup +}=0{endash}7). The analysis of the rotationally resolved PFI-PE bands for O{sub 2}{sup +}({sup 2}{Sigma}{sub u}{sup {minus}},thinspv{sup +}=0thinspandthinsp1) has yielded accurate rotational constants and IE values for these states. The rotational structures resolved in the O{sub 2}{sup +}({sup 2}{Sigma}{sub u}{sup {minus}},thinspv{sup +}=0thinspandthinsp1) PFI-PE bands are contributed overwhelmingly by the {Delta}N={minus}3, {minus}1, +1, and +3 (or {ital N}, {ital P}, {ital R}, and {ital T}) rotational branches, showing that the angular momenta for the outgoing photoelectron are restricted to l=0, 2, and 4. Based on simulation of the observed rotational structures, we also obtain the predissociative lifetimes for O{sub 2}{sup +}(Bthinsp{sup 2}{Sigma}{sub g}{sup {minus}},thinspv{sup +}=0{endash}7) and O{sub 2}{sup +}({sup 2}{Sigma}{sub u}{sup {minus}},thinspv{sup +}=0{endash}1) to be in the range of 0.45{endash}2 ps. {copyright} {ital 1999 American Institute of Physics.}
- OSTI ID:
- 292706
- Journal Information:
- Journal of Chemical Physics, Vol. 110, Issue 1; Other Information: PBD: Jan 1999
- Country of Publication:
- United States
- Language:
- English
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