Line Intensity Measurements of the Band of Ethylene ( 12 C 2 H 4 )

From the four high-resolution FTIR absorbance spectra recorded at a spectral resolution of 0.0063？cm？1, 123 line intensities belonging to the band of 12C2H4 were measured and fit. The upper state rovibrational constants up to sextic terms determined using a Watson's -reduced Hamiltonian model in representation were used to calculate the line intensities of the band. Results of the experimental fit of the line intensities agree well with those obtained by calculations. 1. Introduction Spectroscopists take special interest in ethylene (12C2H4) for its atmospheric and astrophysical importance. Ethylene is naturally present in the atmosphere and is one of several precursors for the formation of tropospheric ozone, a pollutant that has adverse effects on human health. It also has been detected in the atmospheres of the Jovian planets Jupiter, Saturn, Neptune [1–4] and the satellite Titan [5]. Since accurate rotation-vibration parameters and knowledge of line positions and intensities are needed in the detection and monitoring of ethylene in the atmosphere, there have been a number of ethylene studies on the subject in the literature (e.g., [6–10]). As part of our ongoing FTIR investigation of ethylene and its isotopic variants [11–21], determination of the upper state rovibrational constants and line intensity measurements of the -type band of 12C2H4 in the 1820–1950？cm？1 region were performed. The present study aims to contribute to the limited but growing body of knowledge on ethylene line positions and intensities. Previous studies on the band of 12C2H4 include [22–25] which all considered the Coriolis interactions between the band and the and states. Ben Hassen and coworkers [6] measured the absolute line intensities of ethylene in the 1800–2350？cm？1 region. According to a previous paper [25], 39 of the 264 line intensities they measured belonged to the band. In the present study, the upper state rovibrational constants up to sextic centrifugal distortion terms were determined first using a standard Watson’s Hamiltonian model. The derived parameters were then used to calculate line intensities and positions of the band of 12C2H4. From the high-resolution FTIR spectra collected in the laboratory, 123 ethylene line positions and intensities were measured using a peak fitting analysis that implemented the Levenberg-Marquardt algorithm. We found the fit to be satisfactory falling within 6% error when compared to the calculated line intensities. 2. Experimental Details A Bruker 125HR Fourier transform spectrometer located at the FTIR laboratory of the