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Rovibrational structures of isotopic ethylenes by high-resolution Fourier transform infrared (FTIR) spectroscopy
Author
Lebron, Gissella Bahoyo
Supervisor
Tan, Augustine Tuck Lee
Abstract
This thesis investigated the rovibrational structures of ethylene (12C2H4) and five of its isotopic variants: the 13C12CH4 isotopologue, the cis- and trans-C2H2D2 isotopomers, and the C2H3D and C2HD3 isotopologues. Rovibrational analyses of 11 different ethylene bands and integrated band intensity and line intensity measurements of 12C2H4 were carried out. Using a Bruker IFS 125 HR Fourier transform infrared spectrometer, the infrared absorption spectra of the different ethylene bands were measured and recorded with an unapodized resolution of 0.0063 cm-1 at an ambient temperature of 296 K. Four A-type bands of the 12C2H4 molecule were studied in 1820 - 3105 cm-1 spectral region: the ν7 + ν8 band in the 1820 - 1950 cm-1 region; the ν6 + ν10 band in the 1985 - 2100 cm-1 region; and the ν11 and the ν2 + ν12 bands in the 3000 cm-1 region. High resolution spectroscopic work was also performed on the A-type ν12 band of 13C12CH4 in the 1360 - 1520 cm-1 region, the C-type ν7 band of cis- C2H2D2 in the 740 - 950 cm-1 region and the hybrid A-B type ν4 + ν8 band of trans-C2H2D2 in the 1730 - 1940 cm-1 region. In addition, separate high-resolution studies of the hybrid A-B type ν6, the Atype ν3 and the A-type ν12 bands of C2H3D in the 1100 - 1475 cm-1 region and the Ctype ν8 fundamental band of C2HD3 in the 840 - 980 cm-1 region were performed. The single-state rovibrational analyses of the bands were carried out using a standard Watson’s Hamiltonian written in asymmetric reduction and Ir representation to determine each band’s first excited state parameters including the band center, rotational constants and higher-order centrifugal distortion terms. Ground state combination differences analyses performed using the infrared measurements of 13C12CH4, cisC2H2D2, trans-C2H2D2, C2H3D and C2HD3 also yielded accurate ground state parameters for these molecules. Overall, the sets of ground state and first excited state rotational and centrifugal distortion parameters determined from the analyses were more accurate than those reported in the literature. The integrated band intensities of 12C2H4 in the 640 - 3260 cm-1 region were also measured using Fourier transform infrared spectra collected at 0.5 cm-1 resolution and at more than 30 different vapor pressures ranging from 3 x 10-5 to 1 x 10-3 atm. The integrated band intensities of the ν9 and ν2 +ν12 (combined), ν11, ν6 + ν10, ν7 + ν8, ν12 and ν7 and ν10 (combined) bands measured from this study were more accurately determined than those found in the literature. Finally, line intensities of the ν7 + ν8 band of 12C2H4 were also measured using a Voigt profile fitted to each of the 123 peaks considered. The fit was satisfactory and the agreement between the measured and calculated line intensities was within ± 6%. The accurate molecular parameters and other spectroscopic information obtained by this study may be used as reference in modeling the concentration and abundance profile of ethylene in the Earth’s atmosphere and beyond.
Date Issued
2014
Call Number
QC454.F7 Leb
Date Submitted
2014