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States and Spectroscopy of O2+

The spectroscopy of O2+ is well understood and has been studied at high resolution using laser photofragment apparatus [39,40,4,116,123,124,125,126,127]. It is therefore considered to be a `benchmark molecule', from which experimental parameters can be deduced. A recent paper by Ashman et al. [128] to characterise an ion cyclotron trap (ICR) apparatus used O2+  as the molecular ion of choice to characterise the temperature of the molecule inside the trap from the predissociation spectroscopy.
The electronic transition of interest for these experiments is the  ${\rm b^{4}\Sigma_{g}^{-}\leftarrow a^{4}\Pi_{u}}$. All electronic transitions thus far observed in photofragment spectroscopy result in transitions to form ${\rm O(^{3}P_{2}) + O^{+}({^4}S^{0})}$. Rotational levels of the lower electronic state are split into four fine structure components through the spin-orbit interaction, these are $^{4}\Pi_{\frac{5}{2},\frac{3}{2},\frac{1}{2},-\frac{1}{2}}$, and are labelled F1, F2, F3 and F4 respectively. Each rotational component of the ground state is split by lambda doubling, with only negative parity levels present in the homonuclear ${\rm ^{16}O_{2}^{+}}$. Each component is separated by approximately 50 cm-1 from the others (the exact value depending upon the vibrational and rotational states involved). The upper (b $^{4}\Sigma_{g}^{-}$) electronic state has four spin components, labelled:
  ${\rm F_{1}' ~(J'=N'+\frac{3}{2})}$ ${\rm F_{2}' ~(J'=N'+\frac{1}{2})}$ ${\rm F_{3}' ~(J'=N'-\frac{1}{2})}$ and  ${\rm F_{4}' ~(J'=N'-\frac{3}{2})}$. Due to the zero spin of oxygen nuclei and nuclear spin statistics, only odd valued N$^{\prime }$ are present. Transitions between the two electronic states are labelled using the following nomenclature: N $^{\prime}{\rm\Delta J_{F{n}'F{m}''}(J'')}$ Where ${\rm\Delta J}$ is P, Q or R for values of -1, 0, and +1 respectively. The majority of lines observed in the visible region predissociation spectra of O2+  are due to to transitions from v $^{\prime \prime }$=3, 4 and 5 to v$^{\prime }$=3, 4 and 5.


next up previous contents
Next: Experimental Setup Up: Review of O2+ Previous: Introduction   Contents
Tim Gibbon
1999-09-06