Fourier transform spectroscopy using a synchrotron source: Characterization of the instrument line shape and acetylene line parameters around 100 μm

Abstract

The acetylene 100μm spectral region of astrophysical interest was studied to retrieve absolute line positions and intensities of weak hot bands. An absorption path of 150m was used and the spectra were recorded using the far-infrared AILES beamline of the synchrotron SOLEIL and a Bruker IFS 125-HR. To achieve accurate measurements from FT spectra using the full beam of the synchrotron, special cares have been taken into account concerning the apparatus function and especially the optical weighting. The wavenumber dependence of the size of the synchrotron beam was modeled leading to similar results that have been previously obtained for the analysis of the ν5–ν4 band ([8] Jacquemart et al., J Quant Spectrosc Radiat Transfer 2010;111:1223–33) but with a better precision. In the present work, line positions and intensities have been measured for the first time for 816 transitions of 12C2H2 belonging to 17 bands between 51 and 215cm−1. The accuracy of measurements are estimated to be around 0.1×10−3cm−1 for line positions and between 5 and 10% for intensities depending on the strength of the transitions. The spectroscopic knowledge of these hot bands is of importance especially for theoretical and astrophysical applications.