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Title of Thesis

Kamal Ahmed
Institute/University/Department Details
University of Karachi/ Department of Physics
Number of Pages
Keywords (Extracted from title, table of contents and abstract of thesis)
laser-spectroscopy, alkali hydrides, alkali dimers, diatomic molecules, rydberg states, sodium dimmer

Studies in the spectroscopy of diatomic molecules have been undertaken both by classical and laser spectroscopy.

The Classical technique used at the University of Karachi, comprises of absorption studies on a 3.4 m Ebert spectrograph which provides a dispersion of 2.6 A/mm in the second order. A high pressure Xenon arc (450W) serves as the background source. A 2.0 m long steel tube furnace heated by passing around 700 amperes current at 10 volts from a 10 KAV transformer is used. A King type furnace has also been built to be used for obtaining temperatures greater than 1000oC. New Rydberg states of Na2 and K2 dimmers have been observed and A 1∑+ −X1∑+ system of Li, Na and K hydrides Uv region near the dissociation limit have been photographed with direct heating steel tube furnace. Measurements of the spectra have been made by using an Abbe comparator. The wavelengths are converted to vacuum wave numbers by using Edlen’s formula.

Absorption spectra of sodium and potassium molecules have been analysed. A number of new bands in E1∏u←X1∑g system and new rydberg states not previously reposted named as F and H state in both molecules have been investigated. Molecular constants have been evaluated by using computer methods.

Spectra of LiH are analysed involving the ground state X1∑+ (v=1) and the excited state A1∑+ state (v=16 to v=26) Rovibrational constants of extended bands, Dunham coefficient for all observed rovibrational levels and dissociation energy have been evaluated.

In order to pursue the work on alkali dimmers by using laser methods, studies have been made to the University Kaiserslautern, Germany. The UV and visible fluorescence of Na2 and Li2 molecules, selectively excited in a heat-pipe by the frequency doubled radiation of a tunable mode-locked cavity-dumped cw dye laser which delivers nearly Fourier-limited output pulses with 17mW peak power, 500 psec pulse width and 1.5 GHz spectral bandwidth was observed through a monochromator, using time-resolved single-photon counting. The effective lifetimes of directly excited C1∏u state and the collisionally populated 23∏g, 21 ∑+u and 13Δg states have been measured as a function of sodium, lithium vapor pressure and argon pressure which yield the radioactive lifetimes, the population mechanisms and the collisional quenching cross sections of all states in both molecules.

Sodium dimmer formed In a seeded supersonic collimated argon beam is examined with the Doppler-free spectral resolution by crossing the molecular beam perpendicularly with beam of a frequency doubled single-mode, autoscan dye laser. A high resolution fluorescence excitation spectrum in the region 29600-31200 cm-1 have been observed. Three hundred and fifty rotational lines of the Na2 C1∏u (v’=1-11)--X1∑g (v”=0) are assigned. The molecular constants of the C1∏u state are determined and perturbations by the levels in the 2∑u+ state are found. Potential energy curve of this state is constructed using the Rydberg-Klein Rees (RKR) method.

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S. No. Chapter Title of the Chapters Page Size (KB)
1 0 Contents
134.31 KB
2 1 General Introduction 1
46.88 KB
  1.1 Introduction 1
  1.2 Motivation 2
3 2 Spectroscopy Of Diatomic Molecules 6
124.09 KB
  2.1 Tensition Probability 7
  2.2 Band Spectra 9
  2.3 Rotational Spectra 11
  2.4 Dunham Co-Efficients 13
  2.5 Dissociation Energy 15
  2.6 Rydberg States 16
  2.7 Perturbations 17
4 3 Expermntal Procedure 21
91.86 KB
  3.1 Introduction 21
  3.2 Spectrograph 23
  3.3 Vapor Containmnet System 23
  3.4 Senon Arc 29
  3.5 Wavelength Standards (Emission Source 30
  3.6 Measurements 30
5 4 Excited States Of Alkali Dimers 31
139.06 KB
  4.1 Introduction 31
  4.2 Recording Of Spectra 32
  4.3 Vibrational Analysis 34
  4.4 Discussion 41
6 5 Photo-Absorption Studies Of Lih 44
127.31 KB
  5.1 Introduction 44
  5.2 Spectra Of Alkali Hydrides 45
  5.3 Ae— Xe System 47
  5.4 Evaluation Of Dunham Coefficients 50
  5.5 Discussion 52
7 6 Time Resolved Experiment 58
310.7 KB
  6.1 Introduction 58
  6.2 Argon Laser 60
  6.3 Mode-Locking 60
  6.4 Synchronously Mode-Locked Cavity Dumped Dye Laser 65
  6.5 Cavity Dumper 69
  6.6 Second Harmonic Generation 75
  6.7 Febry-Perot Wavemeter 78
  6.8 Heat Pipe 82
  6.9 Measurements 83
  6.10 Single Photon Counting Delayed Coincidence Methos 88
8 7 Time Resolved Laser Spectroscopy Of Alkali Dimers 91
225.76 KB
  7.1 Introduction 91
  7.2 Determinationof Spontaneous Life Time And Quenching Cross Section 94
  7.3 Collision Energy Transfer 96
  7.4 Analysis 97
  7.5 Perturbations Observed Through Life Time Measurements 111
  7.6 Populaltion And Deactivation Mechanisms 112
9 8 Molecular Beam Experiments 117
66.66 KB
  8.1 Introduction 117
  8.2 Supersonic Molecular Beam 118
  8.3 Experiment 118
  8.4 Laser system 121
  8.5 Detection system 123
  8.6 Measurements 123
10 9 High resolution spectroscopy of sodium dimmer 124
116.48 KB
  9.1 Introduction 124
  9.2 Sodium dimmer 125
  9.3 Intensities in rotational transition 125
  9.4 Line identification 127
  9.5 Determination of molecular constants 129
  9.6 Rydberg-Klein-Rees potential 134
  9.7 Dissociation Energy 135
11 10 Conclusion 136
41.21 KB
  10.1 Absorption spectroscopy 136
  10.2 Time resolved laser spectroscopy 137
  10.3 High resolution laser spectroscopy 138
12 11 Appendix 140-155
164.67 KB