The bending of C3: Experimentally probing the [formula omitted]-type doubling and resonance

Abstract

C3, a pure carbon chain molecule that has been identified in different astronomical environments, is considered a good probe of kinetic temperatures through observation of transitions involving its low-lying bending mode (ν2) in its ground electronic state. The present laboratory work aims to investigate this bending mode with multiple quanta of excitation by combining recordings of high resolution optical and infrared spectra of C3 produced in discharge experiments. The optical spectra of rovibronic (Ã1Πu−X̃1Σg+) transitions have been recorded by laser induced fluorescence spectroscopy using a single longitude mode optical parametric oscillator as narrow bandwidth laser source at the University of Science and Technology of China. 36 bands originating from X̃(0v20), v2=0−5, are assigned. The mid-infrared spectrum of the rovibrational ν3 band has been recorded by Fourier-transform infrared spectroscopy using a globar source on the AILES beamline of the SOLEIL synchrotron facility. The spectrum reveals hot bands involving up to 5 quanta of excitation in ν2. From combining analyses of all the presently recorded spectra and literature data, accurate rotational parameters and absolute energy levels of C3, in particular for states involving the bending mode, are determined. A single PGOPHER file containing all available data involving the X̃ and à states (literature and present study) is used to fit all the data. The spectroscopic information derived from this work enables new interstellar searches for C3, not only in the infrared and optical regions investigated here but also notably in the ν2 band region (around 63 cm−1) where vibrational satellites can now be accurately predicted. This makes C3 a universal diagnostic tool to study very different astronomical environments, from dark and dense to translucent clouds.