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Microwave radiation and electron capture in molecular reactions

Akademisk avhandling som med tillst?nd av Stockholms Universitet framl?gges till offentlig granskning f?r avl?ggande av filosofie doktorsexamen fredag den 12 September 2003, Kl 10.00 i sal FD5, Fysikum, AlbaNova universitetscentrum, Roslagstullsbacken 21, Stockholm.

by

Shirzad Kalhori

Doctoral thesis 2003

Molecular Physics Division

Department of Physics

University of Stockholm, Sweden

 

Abstract

This thesis deals with four different topics in physics. In the first part, the design, development and construction of a microwave applicator for chemically reacting samples is reported. We choose the so-called re-entrant cavity to achieve a very intense and an almost homogenous electric field in a gap that of the cavity. The measured quantities for a 5 ml water sample agreed with the calculated values. In the second part of this thesis we have tried to theoretically show that microwaves in the 12.24 cm wavelength region could be absorbed by a liquid phase reaction. The study shows that the microwave photons can be absorbed and the photon energy can be transferred to the motion along the reaction path with the help of a solvent effect. In this study we used a so-called SN2 reaction CH3Cl + Cl- with water molecules. We found that water molecules have torsional vibration eigenfrequencies in this wavelength region. This torsional vibration can with help of the microwave photon energy push the Cl- along the reaction path and increase the reaction rate. The third part of this thesis experimentally shows that an electron captured by an ion lead to molecular dissociation to neutral atoms (or molecules), and also to the formation of ion-pair fragments. The branching ratios and the cross section for dissociative recombination of the poly-atomic molecular ions C2H3+ and C3H7+ under vibrationally relaxed conditions, and for H3+ molecular ion under rovibrationally relaxed condition, to neutral channels and for resonant ion-pair formation are measured. The experiments were performed at the CRYRING (CRYogenic ion source RING) ion storage ring facility, at the Manne Siegbahn Laboratory at Stockholm University. The fourth part is a theoretical calculation of the cross section with help of wave packet method for the ion-pair formation of H3+. In this part we studied the H2+ + H- channel from two possible channels. We used one- and two-dimensional wave packet calculations, where the symmetry changes from D3h to the C2v in the case of one-dimensional calculation. The method and the results are discussed in the thesis.

Stockholm 2003

ISBN 91-7265-717-0

 

This thesis includes the following papers:

Paper I

A re-entrant cavity for microwave enhanced chemistry.

Kalhori S., Elander N., Svennebrink J. and Stone- Elander S.

JMPEE Vol. 38 No: 2, 2003 p. 125

Paper II

Quantum chemical model of an SN2 reaction in a microwave field.

Kalhori S., Minaev B., Stone-Elander S. and Elander N.

(2002), J. Phys. Chem. A, 106, 8516.

Paper III

An enhanced cosmic-ray flux towards ? persei inferred from a laboratory study of the H3+-e- recombination rate.

McCall B. J., Huneycutt A. J., Saykally R. J., Geballe T. R., Djuric N., Dunn G. H., Semaniak J., Novotny O., Al-Khalili A., Ehlerding A., Hellberg F., Kalhori S., Neau A., Thomas R., ?sterdahl F. and Larsson M. (2003), Nature, 422, 500.

Paper IV

Resonant ion-pair formation in electron collisions with rovibrationallycold H3+.

Kalhori S., Al-Khalili A., Ehlerding A., Hellberg F., Neau A., Thomas R., Larsson M., Larson ?., Huneycutt A. J., Djuric N., Dunn G. H., Semaniak J., Novotny O., ?sterdahl F. and Orel A. E.

To be submitted to Phys. Rev. A.

Paper V

Dissociative recombination of C2H3+.

Kalhori S., Viggiano A. A., Arnold S. T., Rosen S., Semaniak J., Derkatch A. M., afUgglas M., and Larsson M. (2002), A & A, 391, 1159.

Paper VI

Rates and products of the dissociative recombination of C3H7+ in lowenergy electron collision.

Ehlerding A., Arnold S. T., Viggiano A. A., Kalhori S., Semaniak J., Derkatch A. M., Rosen S., afUgglas M., and Larsson M. (2003), J. Phys Chem A, 107, N0. 13.

Contents

Chapter 1

1.1 Introduction

Chapter 2

2.1 A microwave applicator.

2.2 Design requirements for the applicator.

Chapter 3 Theoretical methods

3.1 Ab initio methods

3.2 Configuration Interaction method

3.3 Density functional theory

Chapter 4

4.1 SN2 reactions

4.2 Solvent effect and solvated reactions complexes with their vibrational frequencies.

Chapter 5 Electron captures process

5.1 Dissociative recombination

5.2 The resonant ion-pair (RIP) process

Chapter 6

6.1 Experiment

6.2 Corrections

6.2.1 Toroidal correction

6.2.2 Space charge correction

6.2.3 Scintillation detector

6.2.4 The ion sources

 

Chapter 7 Data analysis

7.1 The difficulties of the measurement and calculation of the cross-section

7.2 Measurement of the cross section

7.3 Branching ratios

Chapter 8 The potential curves

8.1 Introduction

8.2 Total Hamiltonian

8.3 Diabatic (crossing) states

8.4 Adiabatic (non-crossing) states

Chapter 9

9.1 Preparation of the calculation for the RIP cross section of H3+

9.2 Direct and indirect coupling between the states

9.3 Rydberg states

Chapter 10

10.1 Calculation of the ion-pair cross section using the wave packet method

Chapter 11 Results and discussion

11.1 A re-entrant cavity for microwave enhanced chemistry.

11.2 Paper II: Solvent effect and microwave induced SN2 reaction.

11.3 Papers III and IV: Cross section measurement in DR, RIP and calculation of ion-pair formation by wave packet method of H3+.

11.4 Dissociative recombination of hydrocarbon ions C2H3+ and C3H7+ papers V and VI.

 

 

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