Least-squares analysis of overlapped bound-free absorption spectra and predissociation data in diatomics: The C(1Πu) state of I2

Abstract

Absorption spectra are recorded at low resolution but high quantitative precision for I(2) vapor at 35 °C and 64 °C. These and literature spectra are analyzed by least-squares quantum spectral simulation of the overlapped A ← X, B ← X, and C((1)Π(u)) ← X transitions, with the aid of a pseudocontinuum model for the discrete regions of the A ← X and B ← X spectra. The analysis yields improved descriptions of the small-R regions of the A- and B-state potentials, which are known precisely at larger R from discrete spectroscopy. The C potential is determined at small R from its C ← X absorption, at intermediate R from literature data for B → C predissociation, and at large R from its known van der Waals well. The estimates of the electronic transition moment function ∣μ(e)(R)∣ for the B-X transition expand upon precise results from a recent determination by a different method. For the C-X and A-X transitions, the R-dependence of the transition moment functions resembles that found previously for these systems in Br(2). Of the spectroscopic properties, the C ← X spectrum is most altered from the previous analysis, being now ∼20% weaker. For B → C predissociation, no derived C potential has yielded computed rates in adequate statistical agreement with the analyzed experimental data.