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J. J. Hillman (University of Maryland), W. E. Blass (University of Tennessee), D. Reuter, D. E. Jennings (NASA/GSFC)
By combining our experimental data with the data of others, these spectra of hydrogen and its isotopic variants will be analyzed simultaneously to obtain a measure of the breakdown of the Born-Oppenheimer approximation. We will employ a variant of the Bunker-Watson extension, which accounts for this breakdown through the nuclear mass dependence of the Dunham coefficients. The first step in this process is to assemble and confirm accuracy of the data set and to assign appropriate statistical weights. Along these lines we have combined our data with the data of others on D2 and H2. A total of 31 D2 lines and 54 H2 were fit to a Dunham expansion. These data were analyzed using a modified version of the iterative bi-weighting, stepwise regression system. Termination of the bi-weighting iterations was controlled by an expected-variance-driven Komolgrov-Smirnov (K-S) test. When a maximum probability that the residuals of the non-zero weighted observations are drawn from a normal distribution is achieved in the bi-weighting iterations, the process is terminated. The maximum probability is often above 90% and the variance of the hypothetical parent distribution is generally quite close to the expected value for the experimental data. The D2 data set was fit to a standard deviation of 0.00163 cm-1, an improvement over current literature fits. The H2 data were fit to a standard deviation of 0.00458 cm-1.
The ultimate goal of this research effort is to obtain a single parameter set which can be used to calculate vibrational-rotational energy levels for H2 and its isotopic variants D2, T2, HD, HT and DT in the 1 \Sigma ground electronic state. This analysis will culminate in the first determination of isotopically invariant vibration-rotation constants for the hydrogen molecule. Such a parameter set does not presently exist to our knowledge. Molecular hydrogen isotopes are of fundamental importance in the molecular sciences, especially molecular astrophysics including stellar, planetary and galactic studies.
This effort has been partially funded by the NASA Planetary Atmospheres Program.
The author(s) of this abstract have provided an email address for comments about the abstract: jhillman@astro.umd.edu
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Bulletin of the American Astronomical Society, 36 #4
© 2004. The American Astronomical Soceity.