The aim of the reported work was two fold; (i) to design and fabricate a three meter off-plane Eagle mounting spectrograph to study the absorption spectra of elements in the region from 1900 to 3450 A and (ii) to investigate the innershell excitation and double excitation spectra of sodium, rubidium and cesium recorded at much higher resolution and dispersion in conjunction with the synchrotron radiation emitted by the 500 MeV electron accelerator, University of Bonn Germany.
The three meter off-plane Eagle mounting spectrograph has been constructed at the atomic and molecular physics laboratory Quaid-i-Azam University Islamabad, Pakistan, which is equipped with a 5000 lines/mm holographic grating, housed in a wooden box to cover the Rowland circle corresponding to the wavelength region between 1900 to 3450 A. An iron arc has been fixed adjacent to the slit of the spectrograph for the reference wavelengths. A high temperature furnace and a high pressure xenon and mercury arc lamps and deuterium lamp served as the background source of continuum, whereas, photographic films are used to record the spectra. The absorption spectra of lithium (up to n = 56), sodium (n = 59) and potassium (n = 51) in the valence shell excitation region have been recorded and a resolution of the order of :t 0.008 A has been achieved.
The innershell and double excitation spectra of sodium, rubidium and cesium have been studied using an identical spectrograph and synchrotron radiation emitted by the 500 Me V electron accelerator as the background source of continuum. In the spectra of sodium investigated in the region from 260 to 400 A we report 200 new levels, in the spectra of rubidium in the region from 500 to 700 A about 130 new levels and in the spectra of cesium in the region from 600 to 900 A about 300 new levels have been found. The observed levels have been arranged in Rydberg series according to the p-inner shell excitation
mp6 (m+ l)s 2S1/2 â†’ mp5(m+ l)s (3p2,1,0, 1p1) ns, nd ,
(where m = 2,4 and 5 for sodium, rubidium and cesium respectively), and to the simultaneous excitation of two electrons, the valence electron and one of the p-subshell electron
mp6 (m+l)s 2S1/2 â†’ mp5 md nl
Rydberg series attaching to the doubly excited ionic levels, eleven in sodium, three in rubidium and four in cesium have been identified. The interchannel interactions among the overlapping series have also been studied using the multichannel quantum defect theory.