Vibrational relaxation in jet-cooled alkyl benzenes. I. Absorption spectra
Fluorescence excitation spectra of a series of alkylbenzenes cooled in a supersonic free jet have been obtained for the first 1000 cm/sup -1/ region of the /sup 1/B/sub 2/(..pi pi..*)reverse arrow/sup 1/A/sub 1/ ultraviolet absorption spectrum. The series includes all n-alkylbenzenes up to n-hexyl together with isopropyl- and tert-butylbenzene. As with toluene, the spectra in this region for all alkylbenzenes is found to be dominated by vibrations of five ring modes: 6a, 6b, 1, 12, and 18a. Three of these: the ''system modes'' (6b, 12, 18a): are found to be largely invariant to changes in the alkyl chain length and type: the ''bath.'' For n-alkylbenzenes with chain length of three or higher, spectra of two distinct conformations are observed with roughly equal intensity. These conformations are distinguished by configuration about the 1--2 carbon--carbon bond of the alkyl chain. When this configuration is trans (n-(t)-alkylbenzene), the alkyl chain extends away from the phenyl ring leaving the ring free to van der Waals complex binding on both sides of the ring. The He/sub 2/--n-(t)-alkylbenzene van der Waals complex is thus observed. When the conformation about the 1--2 bond is gauche (n-(g)-alkylbenzene) the alkyl chain partially covers one side of the phenyl ring. This produces a small red-shift of the spectrum (a self-induced solvent shift) and prohibits the formation of the ring-centered dihelium van der Waals complex.
- Research Organization:
- Rice Quantum Institute
- OSTI ID:
- 5481543
- Journal Information:
- J. Chem. Phys.; (United States), Vol. 72:9
- Country of Publication:
- United States
- Language:
- English
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37 INORGANIC
ORGANIC
PHYSICAL AND ANALYTICAL CHEMISTRY
AROMATICS
ABSORPTION SPECTRA
FLUORESCENCE
ENERGY-LEVEL TRANSITIONS
EXCITATION
VIBRATIONAL STATES
ENERGY LEVELS
EXCITED STATES
LUMINESCENCE
ORGANIC COMPOUNDS
SPECTRA
640302* - Atomic
Molecular & Chemical Physics- Atomic & Molecular Properties & Theory
400301 - Organic Chemistry- Chemical & Physicochemical Properties- (-1987)