Abstract
Line positions and widths of the B 3Π o + u − X 1Σ + g electronic transitions of chlorine and bromine gases are measured in absorption as functions of pressure by means of a scanning Fabry-Perot interferometer spectrometer (resolving power > 10 6). No dependences on quantum numbers are detected. Deconvolutions of measured full-widths-at-half-maxima (FWHM) reveal collision broadening for pressures between 1 and 225 torr. The ratio of self-broadening to shift is always less than that expected for a van der Waals interaction in the impact approximation, namely -2.77. Accordingly, the Lennard-Jones potential is used to determine the effect of the electronic transitions on C 6 and C 12, and there are found 14 and 6% changes in C 6 for Cl 2 and Br 2, respectively. If, instead, one uses the self-broadening only, and a pure van der Waals interaction, the changes are 6 and 5%. Because the effects are in either model unexpectedly small, comparisons are made with less complete measurements (from the literature) for self-broadening in I 2, the B 1Σ + g − X 3Σ - g system of O 2 and the B ′Σ + g − X 1Σ + g system of HD, and for foreign-gas broadening in the A 1Π− X 1Σ system of A1H and the A̋ 1A 2(π ∗, n)−X̋ 1A 1 system of H 2CO as well as the HD system.
Published Version
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