Rotational features in the fluorescence excitation spectrum of O(1D2) from vacuum ultraviolet laser photodissociation of O2

Abstract

Seventh-order anti-Stokes Raman-shifted ultraviolet laser radiation is used to dissociate O2 in the 175–177 nm region of the Schumann–Runge band system, B 3Σ−u–X 3Σ−g. A cross section for the production of O(1D2) is deduced from the 762 nm fluorescence of O2(b 1Σ+g), a collisional de-excitation product of O(1D2) and O2(X 3Σ−g). Step structure observed in the spectrum is attributed to rotational thresholds for absorption from X 3Σ−g to energies above the B 3Σ−u dissociation limit. The threshold energies define a limiting rotationless dissociation energy of 57 136.4±0.9 cm−1. Shape resonances, quasibound by the rotational barrier of B 3Σ−u, are observed for the first time in O2. A theoretical calculation of the cross section is in agreement with the measured cross section when the near-dissociation outer limb of the B 3Σ−u potential has an R−5 long range form. The shape of the adopted potential is consistent with an avoided crossing with another 3Σ−u state near R=4.6 Å.