SPECTROSCOPIC STUDIES OF YTTERBIUM USING LASER AND SYNCHROTRON RADIATION

Sultan, Ahmad (1997) SPECTROSCOPIC STUDIES OF YTTERBIUM USING LASER AND SYNCHROTRON RADIATION. Doctoral thesis, Quaid-i-Azam University, Islamabad.

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Abstract

The spectra of ytterbium have been investigated above and below the first ionization threshold using two different techniques, single photon excitation via synchrotron radiation and multi step resonance ionization spectroscopy. In the synchrotron radiation based experiments, the photoabsorption spectrum in the wavelength region 1200 - 2000 A was recorded in the first order of a 3 meter spectrograph equipped with a 6000 line/mm holographic grating. More than two hundred new levels of YbI are observed, which are interpreted as inner shell transitions 4f446s2 --+ 4f13(2Fs5/2,7/2) nd, ng and doubly excited transitions, 4f446s2 --+ 4f44 5d (2D3/2. 5/2) np, nf and 4f446s2 --+ 4f14 6p(2P1/2 3/2) ns, nd series. All the observed levels lie above the first ionization threshold which are ordered into Rydberg series converging on to six limits. The interchannel interactions between the overlapped series have been parametrized using multichannel quantum defect theory (MQDT). The laser based stepwise excitation experiments on ytterbium are performed using narrow band width dye lasers pumped by a Nd: YAG laser. The thermionic diode which has a very high gain, high sensitivity and good linearity is used for the ion detection. Four different experiments are employed to investigate the high lying odd and even parity levels. First three experiments are performed to record the principal and inter-combination series. Three colour or three photon spectra are compared with the two color three photon spectra below the first ionization. Moreover, we confirmed the different intermediate levels resulting from the single photon and two photon excitations. It is observed that the relative intensities of levels varies in each experiment, revealing strong influence of perturbers. In the other experiment, we have observed the even parity autoionizing resonances in the range of 70700 - 72000 cm-I using three color four photon excitation technique. More than 40 new levels attributable to the inner shell excitation corresponding to the 4f446s2nl Rydberg series are detected. The spectra are analyzed guided by the spectral line shape, parent ion limit and quantum defect approach.

Item Type: Thesis (Doctoral)
Uncontrolled Keywords: ytterbium, synchrotron radiation, laser radiation, single photon excitation, multi step resonance ionization, photoabsorption spectrum, multichannel quantum defect theory, rydberg atoms, innershell excitation
Subjects: Q Science > QC Physics
Depositing User: Muhammad Khan Khan
Date Deposited: 30 Sep 2016 11:28
Last Modified: 30 Sep 2016 11:28
URI: http://eprints.hec.gov.pk/id/eprint/1938

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