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Spectroscopic investigations of inter- and intramolecular processes in crystalline benzene

Citation

Burland, Donald Maxwell (1970) Spectroscopic investigations of inter- and intramolecular processes in crystalline benzene. Dissertation (Ph.D.), California Institute of Technology. http://resolver.caltech.edu/CaltechTHESIS:07212015-114219783

Abstract

I. Introductory Remarks

A brief discussion of the overall organization of the thesis is presented along with a discussion of the relationship between this thesis and previous work on the spectroscopic properties of benzene.

II. Radiationless Transitions and Line broadening

Radiationless rates have been calculated for the 3B1u→1A1g transitions of benzene and perdeuterobenzene as well as for the 1B2u→1A1g transition of benzene. The rates were calculated using a model that considers the radiationless transition as a tunneling process between two multi-demensional potential surfaces and assuming both harmonic and anharmonic vibrational potentials. Whenever possible experimental parameters were used in the calculation. To this end we have obtained experimental values for the anharmonicities of the carbon-carbon and carbon-hydrogen vibrations and the size of the lowest triplet state of benzene. The use of the breakdown of the Born-Oppenheimer approximation in describing radiationless transitions is critically examined and it is concluded that Herzberg-Teller vibronic coupling is 100 times more efficient at inducing radiationless transitions.

The results of the radiationless transition rate calculation are used to calculate line broadening in several of the excited electronic states of benzene. The calculated line broadening in all cases is in qualitative agreement with experimental line widths.

III. 3B1u1A1g Absorption Spectra

The 3B1u1A1g absorption spectra of C6H6 and C6D6 at 4.2˚K have been obtained at high resolution using the phosphorescence photoexcitation method. The spectrum exhibits very clear evidence of a pseudo-Jahn-Teller distortion of the normally hexagonal benzene molecule upon excitation to the triplet state. Factor group splitting of the 0 – 0 and 0 – 0 + v exciton bands have also been observed. The position of the mean of the 0 – 0 exciton band of C6H6 when compared to the phosphorescence origin of a C6H6 guest in a C6D6 host crystal indicates that the “static” intermolecular interactions between guest and hose are different for C6H6 and C6D6. Further investigation of this difference using the currently accepted theory of isotopic mixed crystals indicates that there is a 2cm-1 shift of the ideal mixed crystal level per hot deuterium atom. This shift is observed for both the singlet and triplet states of benzene.

IV. 3E1u1A1g, Absorption Spectra

The 3E1u1A1g absorption spectra of C6H6 and C6D6 at 4.2˚K have been obtained using the phosphorescence photoexcitation technique. In both cases the spectrum is broad and structureless as would be expected from the line broadening calculations.

Item Type:Thesis (Dissertation (Ph.D.))
Subject Keywords:Chemistry
Degree Grantor:California Institute of Technology
Division:Chemistry and Chemical Engineering
Major Option:Chemistry
Thesis Availability:Public (worldwide access)
Research Advisor(s):
  • Robinson, G. Wilse
Thesis Committee:
  • Unknown, Unknown
Defense Date:4 December 1969
Funders:
Funding AgencyGrant Number
CaltechUNSPECIFIED
Shell Companies FoundationUNSPECIFIED
NSFUNSPECIFIED
Record Number:CaltechTHESIS:07212015-114219783
Persistent URL:http://resolver.caltech.edu/CaltechTHESIS:07212015-114219783
Default Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:9066
Collection:CaltechTHESIS
Deposited By: Leslie Granillo
Deposited On:31 Jul 2015 14:47
Last Modified:31 Jul 2015 14:47

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