As the three main non-methane hydrocarbons (NMHC) in the atmosphere, ethane (C2H6), propane (C3H6), and butane (C4H10) provide a testbed for infrared (IR) spectroscopic studies to yield fundamental spectroscopic information both in the mid-infrared (MIR) and in the weak overtone region associated with the near-Infrared (NIR) region of the IR spectrum. In the NIR region, the adoption of long-path FTIR spectroscopic technique utilizing a multipass gas cell increases the sensitivity of a typical commercial FTIR instrument, allowing parts per billion (ppb) detection of the overtone vibrational spectra of C2H6, C3H6, and C4H10. Here, we show the fundamental and overtone (delta ν =2-3 or higher) spectra corresponding to the CH bending and stretching modes of C2H6, C3H6, and C4H10 in MIR and NIR spectral domains. Density functional theory (DFT) wavefunction methods are undertaken to obtain molecular geometry and vibrational frequencies of the molecules to yield theoretical spectra. The calculated IR spectra is used as a tool in assigning the experimental peak positions and intensities, exposing the power of close interplay between theory and experiment in vibrational analysis.

Experimental and theoretical spectroscopic studies of mid and near infrared detection of methane tracers in the environment

254th National Meeting (2017)

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