Spectroscopy and Structure of Jet-Cooled Alpha-Methylstyrene
Abstract
The sterically hindered styrene derivative, alpha-methylstyrene (2- phenyl-propane), is studied by 1-color time-of-flight mass spectroscopy (TOFMS). In contrast to styrene, which has an intense spectral origin transition in the TOFMS, alpha-methyl styrene exhibits a weak origin transition. A progression in a low frequency torsional mode, with an energy level spacing of approx. 69/cm, is built on the origin. The intensity maximum of this progression occurs at the eighth peak position, indicating that the ground and excited state geometries are 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. In the ground state the propenyl group is calculated to be at a approx. 31 deg angle from the plane of the aromatic ring. Analysis of the Franck-Condon intensity profile yields a displacement in the excited state, for the angle between the aromatic and ethylenic groups, of 30 degs relative to the ground state. Alpha- methylstyrene is suggested to be nearly planar in its first excited pi-pi state.
Document Details
- Document Type
- Technical Report
- Publication Date
- Jul 12, 1988
- Accession Number
- ADA197428
Entities
People
- Elliot R. Bernstein
- J. I. Seeman
- V. H. Grassian
Organizations
- Colorado State University