Spectroscopy and Structure of Jet Cooled Alpha-Methylstyrene
Abstract
The ground (S0) and excited (S1) state geometries of alpha- methylstyrene (2-phenylpropene,2) are investigated by mass resolved excitation spectroscopy. In contrast to styrene, which has an intense spectral S1-S0 origin transition, alpha-methylstyrene exhibits a weak origin transition and a long progression in a low frequency torsional mode, with an energy level spacing of approx. 69/cm. The intensity maximum of this progression occurs at the eighth peak position, indicating that the minimum energy geometries of the ground and excited state are considerably displaced from one another. The torsional progression is assigned to the hindered rotation of the propenyl group with respect to the aromatic ring. Based on hot band transitions in the region of the origin, this torsional mode is assigned an energy level spacing of approx. 32/cm in the ground state. Potential parameters derived from an analysis of the spectra are V(2) approx. 0 and V(4) approx. -150/cm for S0 and V(2) = 4867, V(4) = -500 and V(6) = -80/cm for S1. These two derived potential surfaces suggest that alpha-methylstyrene is nearly planar in its first excited singlet state and that the propene group is ca. 45 degs. out of the aromatic plane in its ground state. (aw)
Document Details
- Document Type
- Technical Report
- Publication Date
- Dec 15, 1989
- Accession Number
- ADA216973
Entities
People
- Elliot R. Bernstein
- Henry V. Secor
- J. I. Seeman
- V. H. Grassian
Organizations
- Colorado State University