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Chemical Applications of Infrared Laser Photochemistry


Wight, Charles Albert (1982) Chemical Applications of Infrared Laser Photochemistry. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/gskp-8c88.


Infrared multiphoton electron detachment reactions of gas phase carbanions are investigated using the techniques of ion cyclotron resonance spectroscopy. Ions are spatially confined in a low pressure environment for up to several seconds during irradiation with the unfocused output of a line tunable continuous wave CO2 laser. Analysis of the photodetachment yields as a function of irradiation time, neutral gas pressure, laser intensity and laser wavelength have revealed details of the multiphoton excitation process as well as radiative and collisional relaxation mechanisms. The emphasis for many of these studies is on the wavelength dependence of multiphoton electron detachment yields since the resulting infrared spectra are sensitive probes of molecular structure for distinguishing and identifying isomeric anions. An introduction to low power infrared photochemistry of ions is given in Chapter I.

In Chapter II this technique is used to obtain infrared multiphoton electron detachment spectra of two C7H7- isomers, benzyl and cycloheptatrienyl anions. In the first known example where infrared spectra have been used to probe mechanistic details of an ion-molecule reaction, deprotonation of norbornadiene by CH3O- is shown to yield a mixture of benzyl and cycloheptatrienyl anions.

A closer examination of multiphoton electron detachment kinetics is the subject of Chapter III. The results are interpreted in terms of a kinetic model which is developed to describe low power multiphoton excitation and vibrational relaxation. Radiative relaxation of benzyl anion does not appear to be significant at laser intensities greater than 10 W /cm2 and collisions with neutral molecules are only moderately effective in deactiviating vibrationally excited anions.

Identification of cis and trans butenyl anions in Chapter IV demonstrates the sensitivity of this technique for differentiating molecular structures. Deprotonation of cis-2-butene by NH2- forms the cis anion while deprotonation of trans-2-butene results in a mixture of cis and trans C4H7-. The multiphoton electron detachment spectrum of a third isomer, 2-methylallyl anion, is also presented.

Vibrational relaxation of allyl anion, C3H5- is probed by infrared laser photodetachment techniques in Chapter V. In contrast to the results for benzyl anion in Chapter III, the radiative relaxation of 53 s-1 for allyl anion shows this to be the dominant mechanism for relaxation at pressures below 10-5 torr.

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):
  • Goddard, William A., III
Thesis Committee:
  • Goddard, William A., III (chair)
  • Beauchamp, Jesse L.
  • Dervan, Peter B.
  • Janda, Kenneth C.
Defense Date:22 October 1981
Funding AgencyGrant Number
Record Number:CaltechTHESIS:05172018-114924220
Persistent URL:
Related URLs:
URLURL TypeDescription adapted from Chapter II. adapted from Chapter III. adapted from Chapter IV. adapted from Chapter V.
Default Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:10912
Deposited By: Mel Ray
Deposited On:29 Jun 2018 22:04
Last Modified:16 Apr 2021 22:27

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