Laser Induced Fluorescence of Pb2. Analysis of the Blue-Green System

The blue-green band system of gaseous Pb2 was excited by different Ar+ laser lines. The dense structure of the bands and the fact that natural lead has several isotopes leads to numerous fluorescence series for each exciting line even for narrow laser lines. The fluorescence progressions, which consist of close doublets, were photographed in a 3 m concave grating spectrograph with a resolving power of 180 000. The observed intensities were compared with computed Franck-Condon factors in order to ascertain the vibrational analysis. From observed lines due to rotational relaxation with known change of angular momentum and using isotope relations a set of simultaneous equations that included many fluorescence progressions was built up and a complete rotational and vibrational analysis could be carried out. In the final analysis the ν' numbers range from 0 up to 22, the ν" numbers from 0 up to 19 and the J' numbers up to 306. The first vibrational and rotational constants for the 208Pb2 molecule are (in cm-1) for the lower state: Te" = 0, ωe" = 110.150(6), ωe"χe" = 0.3271(4), Be" = 0.01873(1), αe" = 5.69(1) × 10-5, De" = 2.17 × 10-9 and Te' = 19806.0(1), ωe' = 158.79(8), ωe'ωe' = 1.16(3), Be' = 0.01701(1), αe' = 2.07(2) × 10-5, De' = 1.63(8) × 10-9 for the upper state.

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