M A Baig

High Rydberg transitions in the principal and intercombination series of mercury

The absorption spectrum of mercury vapour has been recorded at high resolution (+or-0.003 AA) in the 1150-1350 AA region with synchrotron radiation as the background source of the continuum. Observations comprise the principal series: 6s2 1S0 to 6snp 1P10 (8<n<or=37) and the intercombination series: 6s2 1S0 to 6snp 3P10 (8<n<or=48). An intensity anomaly occurs at high n values with 3P10 gaining most of the oscillator strength at the expense of the 1P10 transitions. Simple intermediate coupling calculations show that this is due to a change from LS to jj coupling with increasing n values. A two-dimensional Lu-Fano plot it is also presented and this exhibits interchannel interactions between the 1P10 channels. As a result of the new measurements, the previously somewhat uncertain determination of the first ionisation potential is reliably confirmed as 84184.10+or-0.20 cm-1.

Centrifugal barrier effects in the high Rydberg states and autoionising resonances of neon

The photoabsorption spectrum of neon in the range 500-700 AA has been investigated at high resolution using synchrotron radiation and a 3 m normal incidence vacuum spectrograph equipped with holographic gratings. All of the five Rydberg series 2p5(2P32/)ns(3/2)10, nd(1/2)10 and 2p5(1P12/)ns(1/2)10, nd(3/2)10 have been extended to high principal quantum numbers yielding accurate values for the ionisation potentials (2P32/=173 929.6+or-0.2 cm-1 and 2P12/=174 709.8+or-0.2 cm-1). In contrast with the corresponding features of heavier rare gases, the ns-nd interchannel interactions and autoionisation broadening are shown to be weak. The behaviour is discussed with reference to multichannel quantum defect and Hartree-Fock theory, and is shown to result from centrifugal barrier effects in the nd channels.

Rotational analysis of a new electronic transition of HBr and DBr

The authors report new observations at high resolution of the absorption spectra of HBr and DBr using synchrotron radiation as the background continuum source. The new spectra reveal overlapping rotational structure in the region 1100-1200 AA. They have been able to analyse the 1 Sigma -1 Sigma + band originating from the ( sigma 2 pi 3)6p pi configuration. Rotational constants have been determined for both HBr and DBr, and electronic configuration assignments are proposed for most of the bands between 1280 and 1100 AA.

The interchannel interaction between single excitation from 4f14 and double excitation from 6s2 in Yb I

The first observation of a long Rydberg series due to single excitation from the 4f14 subshell in Yb I is reported. A two-channel MQDT analysis reveals a prominent series perturbation due to coupling with one particular 4f145dnf doubly excited series. The Jcj designations of both channels are shown to be consistent with the occurrence of this particular interaction.

Autoionisation resonances in the photoabsorption spectrum of C2H5I

Reports new high-resolution measurements of the photoabsorption spectrum of C2H5I, in which prominent autoionising resonances have been observed. The spectrum is similar in some respects to the reported spectrum of CH3I (Baig et al., 1981). Rydberg series are found to the 2E limits, arising from excitation of a lone-pair pi orbital. The authors have performed a graphical Lu-Fano analysis of the series converging to 2E3/2 by comparison with Xe I and CH3I. The authors are able to extract from their data a quasi-atomic ordering of Rydberg excitations. Above the 2E3/2 threshold, the authors have applied the Dubau-Seaton formula to interpret the spectrum, and they can tentatively ascribe most of the observed width to autoionisation.

On the principal series helium

New measurements of the transition energies of the principal series of helium are reported. They were obtained in a high resolution photoabsorption experiment with synchrotron radiation. It is shown that the wavelength measurements above n=10 are consistent with the more accurate quantum defect extrapolation based on the first nine members to an experimental precision of +or-0.00042 AA.

New high-resolution studies of the 5p spectrum of Ba

New high-resolution measurements of the 5p photoabsorption spectrum of Ba I are reported. The spectral dispersion is fifteen times higher than in the earlier investigation of the same spectrum performed in the laboratory and enables the authors to extend and improve the classification of the complex structure into overlapping Rydberg series. The wavelength calibration was also improved with respect to earlier work by superposing the photoabsorption spectra of He and Ne, which contain many sharp and accurately known transitions, thereby achieving identical illumination of the grating for both the spectrum under investigation and the calibration lines. The continuum source was provided by the 500 MeV electron accelerator in Bonn.

High-resolution photoabsorption spectrum of copper in the 3d subshell excitation region

We report new high-resolution photoabsorption spectra of copper covering the spectral region between 3d subshell excitation using synchrotron radiation as the background source of continuum. The spectra were recorded in the first order of a 3 m spectrograph equipped with a 6000 line/mm holographic grating. Long Rydberg series are observed converging to four conspicuous limits built on the parent ion configurations: The new high-resolution data reveal numerous examples of interchannel interactions and autoionization effects that have been parametrized using the multichannel quantum defect theory.

New high-resolution photoabsorption study of the Lyman bands of H2

The authors report new high-resolution photoabsorption data on the Lyman bands of H2 obtained with a sample at very low vapour density and rather low temperature. The measurements were carried out by synchrotron spectroscopy, using the continuum emitted by the 500 MeV accelerator of the Physikalisches Institut in Bonn. Spectra were recorded in the first order of a 6000 line/mm holographic grating, at a dispersion of 0.6 AA mm-1. More complete photoabsorption data than previously available for the bands from (0,0) to (9,0) are presented and rotational constants are determined. They agree well with the best values in the current literature.

Autoionising Rydberg series in the spectrum of N2

New high-resolution observations of the Hopfield series of autoionising reson- ances in N, are reported. They are discussed in relation to recent ab initio calculations of autoionisation in N,, and are shown to shed further light on variations of quantum defect parameters as a function of n. We are able to analyse two perturbations, one strong (electronic-electronic) and one weak (vibrational-electronic), with the help of simple two-dimensional Lu-Fano plots based on experimental data. The strong perturbation upsets the results of the ab initio theory at high n, but the weak perturbation does not disturb the predictions for lower n, which is consistent with the fact that better agreement between ab initio theory and experiment for line profiles is obtained at low than at high n values.