Franck--Condon factors and r-Centroids for the A ¹∑⁺_u-X¹∑⁺_g Band System of ^107,109Ag₂: Comparison of the Observed and Calculated Absorption Band Strengths

Franck--Condon factors and r-centroids for the A ¹∑⁺_u-X¹∑⁺_g band system of ^{107, 109}Ag₂ are computed using Morse and Rydberg--Klein--Rees potentials for both lower and upper electronic states. The differences between the two sets of results are typically in the third decimal place for transitions involving
vibrational levels with v' and v'' up to about 15. Somewhat larger deviations appear for higher vibrational levels, but both sets of results follow the same pattern, which is to match well with the relative absorption band strength distribution in our experimental spectrum. The relative absorption band strengths are calculated by assuming that the electronic transition moment has only a weak dependence on the internuclear distance r. Good agreement between our measured and calculated absorption band strength ratios is found, which provides an excellent test of the calculated Franck-Condon factors and relative absorption band strengths. The r-centroid value for the (v'=0, v''=0) band is found to be approximately equal to the average value of
r_e' and r_e'', indicating that the potentials of both states are not significantly anharmonic around their minimum regions.