Pakistan Research Repository


Ahmed, Kamal (1994) CLASSICAL AND LASER-SPECTROSCOPY OF ALKALI HYDRIDES AND ALKALI DIMERS. PhD thesis, University of Karachi, Karachi.



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.

Item Type:Thesis (PhD)
Uncontrolled Keywords:laser-spectroscopy, alkali hydrides, alkali dimers, diatomic molecules, rydberg states, sodium dimmer
Subjects:Physical Sciences (f) > Physics(f1)
ID Code:948
Deposited By:Mr. Muhammad Asif
Deposited On:24 Nov 2006
Last Modified:04 Oct 2007 21:03

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