Molecular photoionization as a probe of vibrational–rotational–electronic correlations

Abstract

We determine the rotationally state-resolved 2σu−1 photoionization of N2 into alternative vibrational channels as a function of energy over a 200 eV range. Experiment and theory reveal that Cooper minima highlight the coupling between electronic, vibrational, and rotational degrees of freedom over this very wide range.

Rotationally resolved photoionization: Influence of the 4σ→kσ shape resonance on CO+(B 2Σ+) rotational distributions

“…[30][31][32][33][34][35] In particular, we showed that rotational distributions in N 2 photoionization were strongly influenced by Cooper minima in the lϭ2 partial wave of the 2 u →k g channel over a 250 eV range. [32][33][34][35] An interesting and unexpected result of those previous studies was that the rotationally resolved characteristics of N 2 2 u Ϫ1 and CO 4 Ϫ1 photoionization were qualitatively different for these valence isoelectronic systems. The differences were attributed to qualitative differences in their ionization continua.…”

Vibrational branching ratios in photoionization of CO and N2

“…The high energy behavior results from the strong dependence of the Cooper minima on bond length. 5,6 The low energy region is featureless because there is no shape resonance corresponding to the one observed in CO. This stems from symmetry, i.e., the lϭ3 partial wave is forbidden in the case of N 2 because the final electronic wave function is of gerade symmetry and therefore contains only even partial waves.…”

“…[1][2][3]5 The excursion in the CO vibrational branching ratio curve at h Ϸ35 eV results from the lϭ3 shape resonance in the 4 →k channel. 2,4 The higher energy regime is featureless because there is no shape resonance at higher energies, and the Cooper minima are relatively weak.…”

“…The fluorescence spectra compared well with those obtained previously over a more limited range. 23 The theoretical methods employed in these studies have been discussed previously 5,6 and only a brief discussion is given here. The photoelectron orbitals are obtained using a procedure based on the Schwinger variational principle.…”

“…It was subsequently determined that the Cooper minima in N 2 were strongly R dependent. 5 As a result, these Cooper minima led to a wide-ranging Franck-Condon breakdown, i.e., the vibrational branching ratios for the N 2 ϩ (B 2 ⌺ u ϩ ) state depended on energy, even 200 eV above the ionization threshold. 6 However, there has not been a comparable vibrationally resolved investigation into CO. One expects that the energy dependence of the vibrational branching ratios for CO ϩ (B 2 ⌺ ϩ ) would differ significantly from those of N 2 , as the Cooper minima responsible for the higher energy excursions in N 2 are absent in CO.…”