Absorption cross sections of 13C ethane and propane isotopologues in the 3 µm region

Abstract

To the best of our knowledge, we present first-time measurements of the absorption cross sections of 13C ethane and propane isotopologues in the spectral region around 3000cm-1. The spectra of 13C12CH6, 13C2H6 and 13C12C2H8 have been recorded at approximate room temperature and atmospheric pressure for concentrations between 0.325% and 0.750% in nitrogen using an FTIR spectrometer with a resolution of 0.5cm-1. For calibration purposes an ethane and a propane spectrum each obtained with a natural isotopologue sample were compared to respective spectra from the Pacific Northwest National Laboratory (PNNL). The spectrum of 13C12CH6 is shifted between 3.5cm−1 and 3.8cm-1 towards smaller wavenumbers compared to 12C2H6. The peaks of 13C2H6 ethane were shifted between −4.4cm-1 and −7.2cm-1 relatively to the corresponding 12C peaks. 13C12C2H8 shows a wavenumber shift of −2cm−1 for the largest central peak at 2965.5cm-1 and −6.5cm-1 for the second largest peak at 2955cm-1. The newly determined cross sections will allow for the first time isotopologue-sensitive spectral analyses of ethane and propane in this spectral region and may be used for applications from atmospheric and planetary research to natural gas exploration.