High-resolution study of oscillator strengths and predissociation rates for13C16O and12C18O

Abstract

Models of astronomical environments containing CO require accurate molecular data to reproduce and interpret observations. We conduct experiments at the SOLEIL synchrotron facility to acquire data to model CO photochemistry in the vacuum ultraviolet. The improvement in UV spectroscopic instrumentation in both sensitivity and resolution provides more accurate laboratory spectroscopic determinations. We continue our work on photoabsorption oscillator strengths and predissociation rates for 12 C16 O; we report new measurements for two additional isotopologues, 13 C16 O and 12 C18 O, of four bands from X 1 Σ+ (v′′ = 0) to the v′ = 0–3 vibrational levels of the core-excited W 1 Π Rydberg state and for four overlapping bands (three resolved and one diffuse) between 92.97 and 93.35 nm. Some of the latter include unidentified perturbations. Absorption spectra were recorded using the vacuum-ultraviolet Fourier-transform spectrometer that is installed on the DESIRS beamline at SOLEIL which provides a resolving power R = 350 000. This resolution allows the analysis of individual line strengths and widths in the electronic transitions and the identification of a previously unobserved perturbation in the W(1) level. Gas column densities in the differentially-pumped system were calibrated using the B 1 Σ+ – X 1 Σ+ (v′ = 0,v′′ = 0) band. Absorption bands are analyzed by synthesizing line and band profiles and fitting them to the measured spectra. These considerably improved results are compared with earlier determinations.