Knowledge Bank

A high resolution absorption spectra of the $A3\Pi 1u-X1\Sigma g+$ system of $I2$, consisting of approximately 9700 lines of some 79 bands spanning the vibrational range $v\prime =0-35$ and $v\prime \prime =3-17$, has been recorded and analyzed. A fit to them which uses the previously determined accurate molecular constante for the X-state, yields an accurate new set of molecular constants for the A-state, including the A-doubling constants. The A-state vibrational and inertial rotational constants, as well as mechanically consistent centrifugal distortion constants were represented by near-dissociation expansions. Perturbations due to crossings of level of the $A\prime$-state are observed and assigned.