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A Generalized Theory of Radiationless Transitions


Langhoff, Charles Anderson (1974) A Generalized Theory of Radiationless Transitions. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/ea20-gq57.


The problem of radiationless transitions in polyatomic molecules has been much discussed in recent years. Most attention has been focused on the large energy gap or statistical limit case where the lineshape is Lorentzian and the emission decay exponential. The weighted density of states is assumed to be constant with energy. The broad band approximation, which states that the exciting light uniformly and coherently excites the entire molecular resonance, is standardly employed. The cases of intermediate energy gap have not been extensively investigated. Also, the effect of a finite bandwidth excitation light has only been formally treated. The generalizations proposed here allow the weighted density function to assume general energy dependence. Using the techniques of scattering theory, we are able to present exact formulas for the spectrum and the emission decay which must be evaluated numerically. This enables a more thorough treatment of the intermediate energy gap case where the density is expected to be "line-like". The spectral line shapes become very complex and in no way resemble a Lorentzian. The emission decay curves are correspondingly complex showing quantum beat effects. The ability to detect these quantum beats is also discussed. Also, the excitation band is allowed to have finite width (and, of necessity, a finite time duration). The width and positioning of the excitation band has a dramatic effect on the emission decay. The above generalizations also lead to a new interpretation of the lifetimes of some intermediate case molecules such as NO2, SO2, and CS2. Finally, we apply the formal results to the calculation of the second singlet spectrum of naphthalene in various mixed crystal hosts. We are able to get virtually exact fits to the spectrum using our simple formulas Also, we compute some emission decay curves and compare these curves with some measured gas phase emission curves.

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:
  • Robinson, G. Wilse (chair)
Defense Date:15 November 1973
Additional Information:Pg. 238 is the last page of this thesis.
Funding AgencyGrant Number
Record Number:CaltechTHESIS:06302021-163308263
Persistent URL:
Default Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:14290
Deposited By: Benjamin Perez
Deposited On:02 Jul 2021 16:19
Last Modified:02 Jul 2021 16:20

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