Investigation of four carbon monoxide isotopomers in natural abundance by laser-induced fluorescence in a supersonic jet

The four carbon monoxide (CO) isotopomers ¹²C¹⁶O, ¹³C¹⁶O, ¹²C¹⁸O and ¹²C¹⁷O have been detected simultaneously in a CO gas sample of natural isotopic abundance by measuring rovibronic excitation spectra of six vibronic bands in the Fourth Positive System. The CO sample was flow cooled by adiabatic expansion in a pulsed supersonic jet. The rovibronic excitation spectra were obtained using a novel pulsed laser source (pulse duration ∼25 ns, spectral bandwidth ∼5 GHz) continuously tunable in the 139-155 nm vacuum ultraviolet wavelength region for excitation and recording the total fluorescence. In the present paper we report on the spectroscopic results obtained, including transition wavelengths of three forbidden rovibronic bands (e³Σ⁻ −  X¹Σ⁺(1, 0), d³Δ  − X¹Σ⁺(5, 0), a′³Σ⁺ −  X¹Σ⁺(14, 0)) of ¹²C¹⁶O and band origins of six rovibronic bands (A¹Π(v′ = 0-5) −  X¹Σ⁺(v″ = 0)) of the rare isotopomer ¹²C¹⁷O, and on the experimental conditions facilitating the high sensitivity of the measurements. The exceptional sensitivity demonstrated by the results has been achieved by fine tuning experimental conditions including the conditions in the supersonic expansion, the jet pulse duration and the laser pulse timing.