Multiplet-specific shape resonant features in vibrationally resolved 3σg photoionization of O2

Abstract

We report multiplet-specific vibrationally resolved photoionization cross sections and photoelectron angular distributions for the 3u 8 orbital of 0 2 leading to the v+ = 0-3 levels of the b 4 .1: 8 -and B 2 .1: 8 -states ofOt. These studies were motivated by recent work which shows significant nonstatistical behavior in the vibrationally unresolved spectrum at low photoelectron energies arising from the sensitivity of the ku u shape resonance to the multipletspecific exchange potentials. In addition to the anticipated non-Franck -Condon vibrational distributions arising from the kuu shape resonance, we also find substantial nonstatistical effects in our vibrationally resolved cross sections and particularly in our photoelectron angular distributions over a broad energy range. Extensive electronic autoionization due to Rydberg levels leading to the c 4 .l:u-(2u; 1 ) ion makes it difficult to assess these effects in the available experimental data.

Theoretical studies of cross sections and photoelectron angular distributions in the valence photoionization of molecular oxygen

“…However, these calculations were challenged by more sophisticated multiplet-specific treatment using the iterative Schwinger method. 13,14 The latter calculations obtained two different resonances separated by about 4 eV in the two channels leading to the b 4 ⌺ g Ϫ and B 2 ⌺ g Ϫ ion states, and found a quartet to doublet intensity ratio of more than 15:1 near the threshold. However, these results did not agree with the experiments.…”

“…The photoionization of the 3 g electron has been discussed in a number of theoretical 13,14,36,[40][41][42][43][44] and experimental investigations. [33][34][35] The final configuration of 3 g 1 1 g 2 leads to a number of ion states, including the b 4 ⌺ g Ϫ , B 2 ⌺ g Ϫ , 2 ⌺ g ϩ , D 2 ⌬ g states, among which the photoionization to the b 4 ⌺ g Ϫ and B 2 ⌺ g Ϫ states have most of the intensity.…”

“…13,14 The most prominent one-electron process is the shape resonance which can lead to significant enhancement of the cross section, rapid change in the photoelectron angular distribution ͑asymmetry parameter͒ as a function of photon energy, and/or non-Frank-Condon effects. There are also important multielectron processes, including the autoionization processes via a Rydberg state or valence excited state, shake-up processes and shake-off processes.…”

Relationship between Speed of Lamb Wave and Measurement Error on Distance

“…Computed cross sections by Raseev et al [18] and by Braunstein and McKoy [7] in fact show strong non Franck-Condon e¡ects. This behaviour tends be related to the very narrow shape resonance in the b 4 S À g partial ionization cross section, sv H , caused by the 3s g 3 s u transition yielding maxima in sv H at 20.5, 21.2, 22.0 and 23 eV for v H 0^3, respectively [7]. Actually, 7)).…”

“…The b 4 S À g state of O 2 has been extensively studied both experimentally [4^6] and theoretically [7,8]. The vibrational branching ratio above 20 eV exhibits deviations from the constant Franck-Condon level which was attributed to the 3s g 3 s u shape resonance.…”