Rotationally resolved pulsed field ionization photoelectron study of CO{sup +}(X{sup 2}{Sigma}{sup +},v{sup +}=0{endash}42) in the energy range of 13.98{endash}21.92 eV
- Ames Laboratory, USDOE and Department of Chemistry, Iowa State University Ames, Iowa 50011 (United States)
We have obtained rotationally resolved pulsed field ionization{endash}photoelectron (PFI-PE) spectra of CO in the energy range of 13.98{endash}21.92 eV, covering the ionization transitions CO{sup +}(X&hthinsp;{sup 2}{Sigma}{sup +},v{sup +}=0{endash}42,N{sup +}){l_arrow}CO(X&hthinsp;{sup 1}{Sigma}{sup +},v{sup {double_prime}}=0,N{sup {double_prime}}). The PFI-PE bands for CO{sup +}&hthinsp;(X&hthinsp;{sup 2}{Sigma}{sup +}, v{sup +}=8{endash}22, 24, and 28{endash}39) obtained here represent the first rotationally resolved spectroscopic data for these states. The high-resolution features observed in the PFI-PE spectra allow the identification of vibrational bands for the CO{sup +}&hthinsp;(X&hthinsp;{sup 2}{Sigma}{sup +}, v{sup +}=10, 14, 15, 17, 18, 21, 24, 25, 29{endash}31, 33, 35{endash}37, and 39) states, which strongly overlap with prominent vibrational bands of the CO{sup +}(A&hthinsp;{sup 2}{Pi}{sub 3/2,1/2},B&hthinsp;{sup 2}{Sigma}{sup +}) states. The simulation using the Buckingham{endash}Orr{endash}Sichel model has provided accurate molecular constants for CO{sup +}(X&hthinsp;{sup 2}{Sigma}{sup +},v{sup +}=0{endash}42), including ionization energies, vibrational constants ({omega}{sub e}{sup +}=2218.8{plus_minus}3.5&hthinsp;cm{sup {minus}1}, {omega}{sub e}{sup +}x{sub e}{sup +}=16.20{plus_minus}0.32&hthinsp;cm{sup {minus}1}, {omega}{sub e}{sup +}y{sub e}{sup +}=0.074{plus_minus}0.011&hthinsp;cm{sup {minus}1}, and {omega}{sub e}{sup +}z{sub e}{sup +}={minus}0.001&hthinsp;83{plus_minus}0.000&hthinsp;13&hthin p;cm{sup {minus}1}), and rotational constants [B{sub e}{sup +}=1.9797{plus_minus}0.0051&hthinsp;cm{sup {minus}1}, {alpha}{sub e}{sup +}=0.0201{plus_minus}0.0011thinspcm{sup {minus}1}, {gamma}{sub e}{sup +}=0.000&hthinsp;122{plus_minus}0.000&hthinsp;067&hthinsp;cm{sup {minus}1}, z{sub e}{sup +}={minus}(5.2{plus_minus}1.1){times}10{sup {minus}6}&hthinsp;cm{sup {minus}1}]. Enhancement of {Delta}N{lt}0 rotational branches, attributable to field-induced rotational autoionization, was clearly discernible in PFI-PE bands for CO{sup +}&hthinsp;(X&hthinsp;{sup 2}{Sigma}{sup +}, v{sup +}=0{endash}5, 11, and 12). Significant local enhancements due to near-resonance autoionization were observed for low v{sup +} ({lt}10) PFI-PE bands of CO{sup +}(X&hthinsp;{sup 2}{Sigma}{sup +}), where the density of interloper Rydberg states converging to higher ionic levels is high as manifested in the photoion spectrum. The observation of a long vibrational progression in the Franck{endash}Condon gap region, where strong autoionization states are absent, is consistent with the suggestion that high-{ital n} Rydberg states converging to highly excited vibrational levels of CO{sup +}(X&hthinsp;{sup 2}{Sigma}{sup +}) are partially populated via direct excitation to a repulsive neutral state. The relatively minor band intensity variation observed for high v{sup +} PFI-PE bands is also in accord with the direct excitation model. Since {Delta}N=0, {plus_minus}1, {plus_minus}2, and {plus_minus}3 rotational branches are observed in the PFI-PE spectra, we conclude that the ejected photoelectrons are restricted to angular momentum continuum states l=0{endash}4. {copyright} {ital 1999 American Institute of Physics.}
- OSTI ID:
- 698918
- Journal Information:
- Journal of Chemical Physics, Vol. 111, Issue 19; Other Information: PBD: Nov 1999
- Country of Publication:
- United States
- Language:
- English
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