Jet-Cooled Fluorescence Excitation Spectra and Carbonyl Wagging Potential Energy Functions of Cyclic Ketones in their Electronic Excited States
- 71 Downloads
The jet-cooled fluorescence excitation spectra of 2-cyclopenten-l-one and its 5,5-d2 isotopomer have been recorded in the 370 to 340 nm region. The electronic origin for the undeuterated species occurs at 27210 cm-1 for the S 1(n,π*) electronic excited state. The vibrational frequencies for the three carbonyl motions and the nine ring modes were observed for the excited state. Bands at 67, 158, and 256 cm-1 for the do species, at 63, 147, and 240 cm-1 for the 5-d1 isotopomer, and at 59,138, and 227 cm-1 for the d2 species were assigned to the ring-puckering motion in the S 1 state. A single one-dimensional potential energy function accurately fits the data for all three isotopomers. This function is nearly purely quartic in character and shows the ring to be planar in the electronic excited state. However, it has become less rigid, and this is ascribed to a decrease in initial angle strain within the ring. The C=O and C=C stretching frequencies occur at 1418 and 1357 cm-1 for the do molecule. The ring-twisting frequency for the S 1 state occurs at 274 cm-1. Previous electronic absorption measurements had resulted in a misassignment for this motion.
The jet-cooled fluorescence excitation spectra of the n → π* transitions of cyclopentanone, 3-cyclopenten-l-one, and cyclobutanone have been analysed to determine the vibrational energy spacings in the S 1(n, π) electronic excited states for the out-of-plane carbonyl wagging motions. A double-minimum potential energy function was determined for each and the barriers were found to be 680, 926, and 1940 cmti-1, respectively. The carbonyl wagging angles were determinedto be 22°, 26°, and 41°, respectively. The out-of-plane ring modes were also assigned for each molecule.
KeywordsExcited State Ring Mode Electronic Ground State Electronic Excited State Potential Energy Function
Unable to display preview. Download preview PDF.
- A.D. Walsh: J. Chem. Soc. (1953) 2306.Google Scholar
- J.C.D. Brand: J. Chem. Soc. (1956) 858.Google Scholar
- V.R. Rao and I.A. Rao: Indian J. Phys. 28 (1954) 491.Google Scholar
- CM. Cheatham: Ph.D. Dissertation, Texas A&M University, College Station, Texas (1990).Google Scholar
- D. Chadwick, A.C. Legon, and DJ. Millen: J. Chem. Soc, Faraday Trans. 2 75 (1979) 302.Google Scholar
- B.J. van der Veken: in Vibrational Spectra and Structure, J.R. Durig (Ed.), Marcel Dekker, New York (1986), Vol. 15, pp. 313–400.Google Scholar
- U. Burkett and N.L. Allinger: Molecular Mechanics, American Chemical Society Monograph, Vol. 177, Washington DC, (1982).Google Scholar