Comparison of 12CO+2 and 13CO+2 alignment following photoionization of carbon dioxide

Abstract

Fluorescence polarizations of the B̃ 2Σ+u–X̃ 2Πg (λ∼289 nm) and à 2Πu–X̃ 2Πg (λ>310 nm) transitions in 12CO+2 and 13CO+2 are measured following the photoionization of CO2 at energies ranging from 18.2 to 31 eV. The rotational alignments and channel ratios of the 12CO+2 and 13CO+2 B̃ 2Σ+u state are identical within experimental error and agree well with existing theoretical calculations. Polarizations for the ÖX̃ emission differ for 12CO+2 and 13CO+2. We present evidence that this behavior can be explained by considering the influence of the extensive perturbations in the à and B̃ states of the 12CO+2 photoion. Mixed (Ã, B̃) states in 12CO+2 give rise to red-shifted emission (λ>310 nm) with a quantum yield ΦB, A defined as the fraction of red-shifted emission to all emission originating at the B̃ state energy. Using the present alignment data and published 12CO+2 à and B̃ state fluorescence cross sections, ΦB, A is determined to be nearly independent of ionizing energy with a value of 0.36 at 21.0 eV, in good agreement with other quantum yield measurements.