Resolution of the visible-infrared absorption spectrum of I2 into three contributing transitions

New extinction coefficient measurements are reported for I2 in the region 4200–8000 Å. An argon discharge source is used to estimate the underlying continuum absorption in the banded region. Together with other work these results locate the maximum in the 1 u(1Π) ← XO+g(1Σ) absorption at 4985 Å with a peak extinction of 200 liter mole−1 · cm−1. From the shape of the spectrum the 1u (1Π) potential curve behaves as r−9 in the region of strong absorption. The A1u(3Π)← X absorption is found to be a factor of 2 stronger than previous estimates with a peak extinction of 41 liter mole−1 · cm−1 at 6730 Å. Earlier indications of a linear dependence of the dipole strength on r centroid for the B O+u(3Π)↔ X system are supported in this study. Spectroscopic data for the B↔ X transition are reviewed and new spectroscopic constants recommended for the B state.