OSU Navigation Bar

The Ohio State University University Libraries Knowledge Bank

IDENTIFICATION OF SVL'S OF TWO ISOMERS OF GUAIAZULENE BY POPULATION LABELING SPECTROSCOPY

Please use this identifier to cite or link to this item: http://hdl.handle.net/1811/17755

Show full item record

Files Size Format View
1989-FA-02.jpg 110.2Kb JPEG image Thumbnail of IDENTIFICATION OF SVL'S OF TWO ISOMERS OF GUAIAZULENE BY POPULATION LABELING SPECTROSCOPY

Title: IDENTIFICATION OF SVL'S OF TWO ISOMERS OF GUAIAZULENE BY POPULATION LABELING SPECTROSCOPY
Creators: Bevilacqua, Anthony C.; Kenny, Jonathan E.
Issue Date: 1989
Abstract: In a supersonic expansion, 1,4-dimethyl-7-isopropylazulene (guaiazulene) forms two stable conformers upon the cooling of the rotational degree of freedom of the isopropyl $group^{1}$. This is reflected in the $S_{2}-S_{0}$ fluorescence excitation spectrum which shows two strong origin bands, that of rotamer A being blue-shifted by $106 cm^{-1}$ from the origin of rotamer B. In order to analyze the vibrational structure of the $S_{2}$ state of guaiazulene, a methodology is needed to distinguish the vibrations of each rotamer. Identification by searching the spectrum for pairs of transitions separated by $106 cm^{-1}$ is not always correct or useful. Utilizing jet conditions, we have employed an optical-optical double resonance technique. A pulsed (5 nsec) dye laser $(\nu_{1})$ is resonant with the $O_{0}^{0}$ band of one rotamer, say rotamer B. This depopulates the $S_{0} O_{0}$ level of rotamer B via electronic excitation. Another pulsed dye laser $(\nu_{2})$ is tuned to an SVL in the $S_{2}\leftarrow S_{0}$ excitation spectrum, an SVL whose molecular conformation is unknown. The OODR signal from this SVL is reported as the difference of sample ($\nu_{1}$ off, $\nu_{2}$ on) and blank ($\nu_{1}$ on $\nu_{2}$ on) fluorescence resulting from the $\nu_{2}$ excitation. When the unknown SVL is a member of the rotamer A manifold, there is no distinction between sample and blank; the fluorescence intensity of an SVL of A is independent of the concentration (or ground state population) of rotamer B. However, when the SVL belongs to the rotamer B structure, differences of up to 60\% are observed. This is due to the depopulation of the $O_{0}$ level of B by $\nu_{1}$, resulting in less fluorescence intensity derived from $\nu_{2}$. This population labeling experiment unambiguously assigns each SVL and also show that only tow conformers exist under our experimental conditions.
URI: http://hdl.handle.net/1811/17755
Other Identifiers: 1989-FA-2
Bookmark and Share