ANALYSIS OF A AND E COMPONENTS OF THE ν₂₁ TORSIONAL FUNDAMENTAL OF PROPENE AT 188 cm−¹

Groner, Peter

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Title

ANALYSIS OF A AND E COMPONENTS OF THE ν₂₁ TORSIONAL FUNDAMENTAL OF PROPENE AT 188 cm−¹

Author(s)

Groner, Peter

Contributor(s)

• Western, Colin
• Zhao, Jianbao
• Billinghurst, Brant E.
• Daunt, Stephen J.

Issue Date

2023-06-19

Keyword(s)

• Large amplitude motions
• internal rotation

Abstract

The far infrared spectrum of propene, CH₃ − CH = CH₂, has been measured at 193.65 K with a resolution of 0.00096 cm−¹on the FIR beamline at the Canadian Light Source (CLS) synchrotron. The torsional fundamental band ν₂₁ at 188 cm−¹is quite complex because the coupling of the angular momenta of the overall rotation with the internal rotation of the CH₃ group splits every rovibrational energy level (without internal rotation) into an A- and an E-component. As a result, every rovibrational transition splits into two or three components. To predict and assign the spectrum and to determine spectroscopic constants by the LS method, the ERHAM program ᵇ has been modified to use it for rovibrational spectra. Initially, the spectroscopic constants for the ground state (GS) were fixed at the values determined by Craig et al.ᶜ from almost 900 microwave and millimeter-wave frequencies. This was good enough to begin the assignment of transitions of ν₂₁ involving low Kₐ levels. However, for Kₐ > 3, the ratio of the standard deviation over the estimated experimental uncertainty increased with increasing Kₐ despite the introduction of additional tunneling parameters. Only the inclusion of the internal rotation parameters ρ and β (which had been held constant with the GS constants) among the variable parameters brought the standard deviation down to an acceptable level. From then on, the transitions of ν₂₁ were used simultaneously with all GS transitions (footnote b) to fit the parameters of two different effective internal rotation Hamiltonians (one each for the GS and ν₂₁ levels) but with shared ρ and β. More than 6000 individual transitions (J up to 50, K up to 8) have been assigned so far for the ν₂₁ band and preliminary constants have been obtained, among ved internal rotation barrier.

Publisher

International Symposium on Molecular Spectroscopy

Type of Resource

Text

Language

eng

Handle URL

https://hdl.handle.net/2142/122448

DOI

https://doi.org/10.15278/isms.2023.6753

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