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DEVELOPMENT AND IMPLEMENTATION OF METHODS
FOR SLICED VELOCITY MAP IMAGING.
STUDIES OF OVERTONE-INDUCED DISSOCIATION AND
ISOMERIZATION DYNAMICS OF HYDROXYMETHYL RADICAL
(CH2OH AND CD2OH)
by
Mikhail Ryazanov
A Dissertation Presented to the
FACULTY OF THE USC GRADUATE SCHOOL
UNIVERSITY OF SOUTHERN CALIFORNIA
in Partial Fulfillment of the
Requirements for the Degree
DOCTOR OF PHILOSOPHY
(CHEMISTRY: CHEMICAL PHYSICS)
December 2012
Copyright 2012 Mikhail Ryazanov
Object Description
| Title | Development and implementation of methods for sliced velocity map imaging. Studies of overtone-induced dissociation and isomerization dynamics of hydroxymethyl radical (CH₂OH and CD₂OH) |
| Author | Ryazanov, Mikhail |
| Author email | ryazanov@usc.edu;mikhail.ryazanov@gmail.com |
| Degree | Doctor of Philosophy |
| Document type | Dissertation |
| Degree program | Chemistry (Chemical Physics) |
| School | College of Letters, Arts And Sciences |
| Date defended/completed | 2012-07-23 |
| Date submitted | 2012-11-13 |
| Date approved | 2012-11-14 |
| Restricted until | 2012-11-14 |
| Date published | 2012-11-14 |
| Advisor (committee chair) | Reisler, Hanna |
| Advisor (committee member) |
Wittig, Curt Haas, Stephan |
| Abstract | An experimental setup for sliced velocity map imaging (SVMI) of H fragments produced in photodissociation of small molecules and radicals is designed, constructed and characterized experimentally. The setup uses an ion-optical arrangement consisting of an accelerator that allows creation of variable electrostatic field geometries near the photodissociation region (where the studied fragments are produced) for initial acceleration and focusing of the ionized fragments and an additional electrostatic lens inside the drift tube for independent control of the optical magnification. This approach permits largely independent control of the radial and temporal characteristics of the velocity mapping, making it possibile to achieve time-gated slicing with selectable relative thickness for a very broad range of fragment kinetic energies (from a fraction of an electronvolt to a few electronvolts)—an important capability not available in other SVMI setups described in the literature. At the same time, the kinetic energy resolution (∼1%) obtainable in a large part of the operating range is comparable to that of the best known SVMI setups. ❧ Two methods for analysis of the raw data produced in VMI and SVMI experiments are developed and implemented. The first method is intended for correction of small distortions of raw velocity map images. It is shown that correction of these distortions, easily achievable by processing of the image using this method, might significantly increase the effective resolution for the speed or kinetic energy distribution extracted from the image. In addition, artifacts in angular distributions, produced by the distortions, are eliminated in the corrected images. The method is universal, being able to correct almost arbitrary distortions, and can be applied to full-projection and sliced velocity map imaging data represented as coordinate lists and as raster images. ❧ The second data-processing method allows reconstruction of SVMI data recorded with slicing pulses of arbitrary shape and relative thickness (including the fullprojection VMI as a trivial particular case). This ability permits to exploit the improved signal-to-noise ratio of the SVMI method and at the same time achieve the best resolution over the whole imaged velocity range, impossible with finite slicing without reconstruction. Testing of the method on synthetic and experimental images demonstrated that the results obtained by reconstruction of sliced images outperform the results from sliced images without reconstruction and from Abel inversion of full-projection images in terms of the resulting signal-to-noise ratio and resolution simultaneously. ❧ The developed and implemented setup and methods were successfully used in studies of overtone-induced dissociation and isomerization dynamics of hydroxymethyl radial CH₂OH and its isotopolog CD₂OH. While these studies, at first glance, largely repeat the previous work, the new experimental capabilities in the present work, significantly improving the resolution and detection efficiency, allowed to obtain quantitative and qualitative results at a completely new level. In particular, interaction of the third O–H stretch overtone (4v₁ level) with a combination of O–H and antisymmetric C–H stretches (3v₁ + v₂ level) was observed for the first time. Dissociation of the vibrationally excited radical to formaldehyde and hydrogen fragments (CH₂OH→CH₂O + H) was observed from both of these levels. In case of CD₂OH excitation (for which only the 4v₁ level was observed), in addition to the H products, a small amount of D fragments correlating with CHDO cofragments was observed for the first time, providing an explicit experimental demonstration of the CD₂OH→CHD₂O→D + CHDO decomposition through isomerization to the methoxy radical. Analysis of the vibrational distributions of the formaldehyde products in all reactions suggests that while O–H bond fission is responsible for the major part of the produced H fragments, a noticeable part of them in CH₂OH and CD₂OH decomposition is also due to the isomerization pathway. The relatively high kinetic energy resolution in the present experiments allowed an accurate direct determination of the hydroxymethyl dissociation energies: D₀(CH₂OH→CH₂O + H) = 10160±70 cm⁻¹, D₀(CD₂OH→CD₂O + H) = 10135±70 cm⁻¹, D₀(CD₂OH→CHDO + D) = 10760±60 cm⁻¹. |
| Keyword | hydroxymethyl radical; inverse Abel transform; isomerization; sliced velocity map imaging; vibrational predissociation |
| Language | English |
| Part of collection | University of Southern California dissertations and theses |
| Publisher (of the original version) | University of Southern California |
| Place of publication (of the original version) | Los Angeles, California |
| Publisher (of the digital version) | University of Southern California. Libraries |
| Provenance | Electronically uploaded by the author |
| Type | texts |
| Legacy record ID | usctheses-m |
| Contributing entity | University of Southern California |
| Rights | Ryazanov, Mikhail |
| Access conditions | The author retains rights to his/her dissertation, thesis or other graduate work according to U.S. copyright law. Electronic access is being provided by the USC Libraries in agreement with the author, as the original true and official version of the work, but does not grant the reader permission to use the work if the desired use is covered by copyright. It is the author, as rights holder, who must provide use permission if such use is covered by copyright. The original signature page accompanying the original submission of the work to the USC Libraries is retained by the USC Libraries and a copy of it may be obtained by authorized requesters contacting the repository e-mail address given. |
| Repository name | University of Southern California Digital Library |
| Repository address | USC Digital Library, University of Southern California, University Park Campus MC 7002, 106 University Village, Los Angeles, California 90089-7002, USA |
| Repository email | cisadmin@usc.edu |
| Archival file | uscthesesreloadpub_Volume4/etd-RyazanovMi-1291.pdf |
Description
| Title | Page 1 |
| Contributing entity | University of Southern California |
| Full text | DEVELOPMENT AND IMPLEMENTATION OF METHODS FOR SLICED VELOCITY MAP IMAGING. STUDIES OF OVERTONE-INDUCED DISSOCIATION AND ISOMERIZATION DYNAMICS OF HYDROXYMETHYL RADICAL (CH2OH AND CD2OH) by Mikhail Ryazanov A Dissertation Presented to the FACULTY OF THE USC GRADUATE SCHOOL UNIVERSITY OF SOUTHERN CALIFORNIA in Partial Fulfillment of the Requirements for the Degree DOCTOR OF PHILOSOPHY (CHEMISTRY: CHEMICAL PHYSICS) December 2012 Copyright 2012 Mikhail Ryazanov |
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