Resonances in the photodissociation of isotopic molecular oxygen—I. The longest band

We present detailed photoabsorption cross section measurements of the (0-0) and (0–1) bands of the E 3∑ - u - X 3∑ - g transition of molecular oxygen. The isotopes 16O 2, 16O 18O and 18O 2 were studied at 79 and 295 K, with an instrumental resolution of 0.04–0.06 Å FWHM. Our results show clearly that these bands provide one of the rarely observed examples of Beutler-Fano resonances in molecular photodissociation. With the aid of empirical modelling, we show that the widths and asymmetries of individual lines vary significantly with rotation and isotopic mass, but the oscillator strengths show no isotope effect.