Ammonia: Dynamical modeling of the absorption spectrum

A quantum mechanical calculation involving a time-dependent formalism is used to study the ÖX̃ transition in ammonia. The experimental spectrum exhibits a single progression in the bend despite evidence that there is a displacement in both the bond lengths and bond angles in going from the ground to first excited state. Two models for the excited state surface are presented which reproduce this single progression in the bend. The starting point for our study is an ab initio surface. The excited state surface is first adjusted to match the equilibrium geometries and rotational constants derived from experiment. The surface is then further refined to produce agreement with the experimental absorption and emission frequency and intensity patterns.