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Rovibrational studies of ethylene and formaldehyde isotopologues by high-resolution Fourier transform infrared (FTIR) spectroscopy
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Type
Thesis
Author
Ng, Alicia Li Ling
Supervisor
Tan, Augustine Tuck Lee
Abstract
This thesis presents the details of the experimental work that has been done on ethylene and formaldehyde, and a brief introduction to the theoretical background of the project including the principles of the Fourier transform infrared spectroscopy. The research work aims to investigate the rotation-vibrational structures of four isotopologues of ethylene (12C2H4) and one of formaldehyde (H212CO) through conducting experimental work and rovibrational analyses on: 1) the C-type ν8 and A/B-type 2ν8 bands of C2HD3, 2) the A-type ν12, B-type ν10 and C-type ν7 bands of cisC2H2D2, 3) the A/B hybrid ν12 band of trans-C2H2D2, 4) the C-type ν8 band of 13C2HD3,
and 5) the A-type ν2 and ν3 bands of H213CO. Using Bruker IFS 125 HR Fourier transform infrared spectrometers, the infrared absorption spectra of selected ethylene and formaldehyde isotopologues were recorded at unapodized resolutions of 0.0063 cm-1 or 0.00096 cm-1.
All rovibrational analyses were carried out using Watson’s A-reduced Hamiltonian in the Ⅰr representation. For 12C2HD3 the ν8 = 1 and ν8 = 2 states were found to be coupled by a- and b-type Coriolis interactions with the ν6 = 1 and the ν3 = ν4 = 1 states respectively. In cis-C2H2D2 the ν10 band of was observed to be globally perturbed by the ν8 band through b-type Coriolis resonance while some absorption lines of the ν12 band were found to deviate from their unperturbed positions due to local energy level crossings via c-type Coriolis resonance with the nearby 2ν10 band. Lastly anharmonic resonance was observed to link rotational energy levels of ΔKa = ±2 between the v2 = 1 and v3 = 1 states of H213CO. Except for the c-Coriolis resonance between the ν12 and 2ν10 bands of cis-C2H2D2, other resonance interactions (ν10 of cis-C2H2D2, ν8 and 2ν8 of 12C2HD3, and ν2 and ν3 of H213CO) were analysed for the first time. In the dual-state rovibrational analyses of the perturbed bands, resonance operators were included off-diagonal in v-blocks in the Hermitian Hamiltonian. All upper state parameters derived from the investigations of the infrared active states include the band center, three rotational constants and centrifugal distortion constants. Some rovibrational constants of unobserved perturbing bands could be derived together with the resonance parameters.
Rovibrational analyses of the Rovibrational analyses of the ν8 band of 12C2HD3, ν12 band of cis-C2H2D2, ν12 band of trans-C2H2D2 and ν2 band of H213CO resulted in improved rovibrational constants over those previously reported in the literature. Investigations into the rovibrational structures of 2ν8 of 12C2HD3, ν10 of cis-C2H2D2, ν8 of 13C2HD3 and ν3 of H213CO produced previously-unreported sets of molecular parameters for these states.
Ground state combination differences were performed from the infrared measurements to determine the rotational and centrifugal distortion constants for the ground states of all four isotopologues of ethylene included in this thesis. The ground state constants for 12C2HD3, cis-C2H2D2 and trans-C2H2D2 determined from this work were improved over previous works. For 13C2HD3 ground state constants derived here were reported in the literature for the first time. Additionally, the ground state rovibrational parameters of 12C2HD3 and cis-C2H2D2 determined were found to be in close agreement to theoretically calculated values using CCSD(T)/cc-pVTZ, MP2/ccpVTZ and B3LYP/cc-pVTZ levels of theory. The molecular parameters obtained in this study would provide a better understanding and knowledge of the molecular structures of the ethylene and formaldehyde molecules.
and 5) the A-type ν2 and ν3 bands of H213CO. Using Bruker IFS 125 HR Fourier transform infrared spectrometers, the infrared absorption spectra of selected ethylene and formaldehyde isotopologues were recorded at unapodized resolutions of 0.0063 cm-1 or 0.00096 cm-1.
All rovibrational analyses were carried out using Watson’s A-reduced Hamiltonian in the Ⅰr representation. For 12C2HD3 the ν8 = 1 and ν8 = 2 states were found to be coupled by a- and b-type Coriolis interactions with the ν6 = 1 and the ν3 = ν4 = 1 states respectively. In cis-C2H2D2 the ν10 band of was observed to be globally perturbed by the ν8 band through b-type Coriolis resonance while some absorption lines of the ν12 band were found to deviate from their unperturbed positions due to local energy level crossings via c-type Coriolis resonance with the nearby 2ν10 band. Lastly anharmonic resonance was observed to link rotational energy levels of ΔKa = ±2 between the v2 = 1 and v3 = 1 states of H213CO. Except for the c-Coriolis resonance between the ν12 and 2ν10 bands of cis-C2H2D2, other resonance interactions (ν10 of cis-C2H2D2, ν8 and 2ν8 of 12C2HD3, and ν2 and ν3 of H213CO) were analysed for the first time. In the dual-state rovibrational analyses of the perturbed bands, resonance operators were included off-diagonal in v-blocks in the Hermitian Hamiltonian. All upper state parameters derived from the investigations of the infrared active states include the band center, three rotational constants and centrifugal distortion constants. Some rovibrational constants of unobserved perturbing bands could be derived together with the resonance parameters.
Rovibrational analyses of the Rovibrational analyses of the ν8 band of 12C2HD3, ν12 band of cis-C2H2D2, ν12 band of trans-C2H2D2 and ν2 band of H213CO resulted in improved rovibrational constants over those previously reported in the literature. Investigations into the rovibrational structures of 2ν8 of 12C2HD3, ν10 of cis-C2H2D2, ν8 of 13C2HD3 and ν3 of H213CO produced previously-unreported sets of molecular parameters for these states.
Ground state combination differences were performed from the infrared measurements to determine the rotational and centrifugal distortion constants for the ground states of all four isotopologues of ethylene included in this thesis. The ground state constants for 12C2HD3, cis-C2H2D2 and trans-C2H2D2 determined from this work were improved over previous works. For 13C2HD3 ground state constants derived here were reported in the literature for the first time. Additionally, the ground state rovibrational parameters of 12C2HD3 and cis-C2H2D2 determined were found to be in close agreement to theoretically calculated values using CCSD(T)/cc-pVTZ, MP2/ccpVTZ and B3LYP/cc-pVTZ levels of theory. The molecular parameters obtained in this study would provide a better understanding and knowledge of the molecular structures of the ethylene and formaldehyde molecules.
Date Issued
2019
Call Number
QD305.H7 Ng