Predictive theory for widths of hemoglycin optical absorption features

Develop a predictive theoretical framework that determines the spectral widths (e.g., full width at half maximum) of the ultraviolet and visible absorption features of hemoglycin, including the nominal 218–219 nm UV bump and the visible bands near 480 nm and 650 nm, from microscopic damping processes without relying on ad hoc assumptions.

Background

Using quantum chemistry (RPA) and a dielectric response model, the paper reproduces the positions and relative strengths of key hemoglycin absorptions and their contribution to interstellar extinction, but it assumes a damping proportional to transition frequency to set linewidths.

The authors explicitly state that their present theory cannot predict the widths of these absorptions, indicating the need for a more complete model that includes vibrational, rotational, and electronic coupling effects responsible for damping.