D. F. T. Mullamphy

Collisional broadening of alkali doublets by helium perturbers

We report results for the Lorentzian profiles of the Li I, Na I and K I doublets and the Na I subordinate doublet broadened by helium perturbers for temperatures up to 3000 K. They have been obtained from a fully quantum-mechanical close-coupling description of the colliding atoms, the Baranger theory of line shapes and new ab initio potentials for the alkali–helium interaction. For all lines except the 769.9 nm K I line, the temperature dependence of the widths over the range 70 ≤ T ≤ 3000 K is accurately represented by the power law form w = aTbb with 0.38 < b < 0.43. The 769.9 nm K I line has this form for 500 ≤ T ≤ 3000 K with b having the higher value of 0.49. Although the shifts have a more complex temperature dependence, they all have the general feature of increasing with temperature above T ~ 500 K apart from the 769.9 K I line whose shift decreases with temperature.

Self-broadening of triplet lines of helium

The self-broadening of the helium triplet lines 23S1-33P2,1,0, 23P2,1,0-n3S1 and 23P2,1,0-n3D3,2,1 for n=3 4, 5 at temperatures of 80 K and 300 K is calculated using a semi-classical impact model of pressure broadening. The collision between the excited helium emitter and ground state helium perturber is described in terms of adiabatic molecular potentials based upon model potential expressions for the interacting atoms. For the triplet lines for which experimental results are available, the calculated widths are too high by an average of 20%. However, imposition of a lower cutoff on impact parameters in order to exclude perturber paths entering classically forbidden regions of the interaction significantly improves the agreement with experiment.

Alkali Line Shapes for the Spectra of Brown Dwarfs

Highly accurate calculations of the central cores of pressure broadened alkali resonance doublets due to H2 and He perturbers are needed in order to estimate the effects of dust in brown dwarf atmospheres. We report results for the Lorentzian profiles of the Na I and K I doublets broadened by helium perturbers for temperatures up to 3000 K. They have been obtained from a fully quantum‐mechanical close‐coupling description of the colliding atoms, the Baranger theory of line shapes and new ab initio potentials for the alkali‐rare gas interaction.

Unification of the Impact and One‐Perturber Theories of Line Shapes

It is shown that one‐perturber theory can be rewritten into a form from which the quantity that directly corresponds to the width of the line as calculated from the impact approximation can be extracted. The theory uses a full quantum mechanical description of the emitter‐perturber system and line widths for the lithium resonance lines broadened by helium have been calculated using both impact and one‐perturber theory for the temperature range 0.1⩽T⩽3000 K. Agreement is excellent for T⩾20 K.

Recent Work on Line Shapes for the Spectra of Cool Stars

Accurate pressure broadened profiles of alkali resonance doublets perturbed by helium are needed for modelling of the atmospheres of late M, L and T type brown dwarfs for temperatures up to 3000 K. Previous fully quantum‐mechanical calculations of line widths and shifts are extended to consider the line‐wing profiles where impact theory is no longer valid. Results are presented for the Lorentzian line widths of the lithium, sodium and potassium resonance lines calculated using both impact and one‐perturber theory. Excellent agreement between these two approximations is obtained, demonstrating that quantum‐mechanical calculations of the line profiles can be made that are accurate over the whole range of frequencies from the line centre to the line wings.

Self-broadening of - ( n = 5,6) neon lines

Quantum close-coupled calculations of the collisional self-broadening of neon lines involving transitions whose upper level is either , , or and lower level is , , or are presented for temperatures between 70 and 400 K. These calculations are based on the quantum-mechanical impact theory of Baranger in which the interatomic interaction is represented by adiabatic molecular potentials calculated using model potentials for the electron - atom and atomic core - core interactions. We discuss the complications arising from the contributions of the highly excited states and give parametric fits to the width and shifts of all lines in the temperature range 70 - 400 K.

Pressure broadening of 2p53s−2p53p neon lines

We present a detailed theoretical calculation of collisional self-broadening in neon where the lower level is either a metastable or intercombination level, 3s′[12]0 or 3s[32]1,2, and the upper level is 3p′[12]1, 3p′[32]1,2, 3p[12]0,1, 3p[32]1,2, or 3p[52]2. The collisionally broadened width and shift are obtained for the temperature range 70 K to 370 K under the impact approximation using realistic interaction potentials and a fully quantum mechanical model of the scattering event. Parametric fits to the temperature dependence of the width and shift are reported which can be used to reproduce the theoretical results to within 0.5%.

Self-broadening of 2p53p-2p53d neon lines

A quantum close-coupled calculation of the collisional broadening of the 3p[1/2]1-3d[1/2]0,1 neon transitions is presented. The calculations are based on the quantum-mechanical impact theory of Baranger and represent the interatomic interaction by adiabatic molecular potentials calculated using model potentials for the electron-atom and atomic core-core interactions. The close-coupled equations are solved using a R-matrix method and results obtained for temperatures between 70 and 400 K. For 298 K the calculated widths agree closely with the experimental results of Ciurylo et al (1994 J. Phys. B: At. Mol. Opt. Phys. 27 4181-93), thus providing support for their analysis procedure which incorporated the effects of non-thermalized emitters. The calculated shifts at 298 K are positive for both lines, in contrast with the experimental situation where the 754.4 nm line was found to have a positive shift and the 753.5 nm line had a negative shift.

Self-broadening of non-resonance - neon lines

Quantum close-coupled calculations of the collisional self-broadening of neon lines involving transitions whose lower level is either a metastable or intercombination level, and , and upper level is , or are presented for temperatures of 77 and 273 K. These calculations are based on the quantum-mechanical impact theory of Baranger in which the interatomic interaction is represented by adiabatic molecular potentials calculated using model potentials for the electron - atom and atomic core - core interactions. Semiclassical calculations for lines involving transitions between these lower levels and either or at temperatures of 77 and 273 K are given and compared with the recent quantum close-coupled calculations of these lines by Leo et al (1995 28 4449 - 58). Also reported are parametric fits to the temperature dependence of the line widths and shifts in the quantal model for transitions from the and 3p levels to the metastable and intercombination levels for the temperature range 70 - 370 K.