Theoretical study of electronic absorption spectroscopy of propadienylidene molecule vis-â-vis the observed diffuse interstellar bands

► Theoretical study of spectroscopy and dynamics of electronically excited l-C3H2. ► Construction of ab initio electronic potential energy and diabatic coupling surfaces. ► First principles study of nuclear dynamics on excited electronic states. ► Findings reveal l-C3H2 is a potential molecular carrier of diffuse interstellar bands. ► Electronically excited l-C3H2 decays by ultrafast nonradiative internal conversion.