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

Observation of broad and diffuse interstellar bands (DIBs) at 4881 and 5440 assigned to the optical absorption spectrum of Y-shaped propadienylidene (H ₂CCC:) molecule is theoretically examined in this paper. This molecule apparently absorbs in the same wavelength region as the observed DIBs and was suggested to be a potential carrier of these DIBs. This assignment mostly relied on the experimental data from radioastronomy and laboratory measurements. Motivated by these available experimental data we attempt here a theoretical study and investigate the detailed electronic structure and nuclear dynamics underlying the electronic absorption bands of propadienylidene molecule. Our results show that this molecule indeed absorbs in the wavelength region of the recorded DIBs. Strong nonadiabatic coupling between its energetically low-lying electronic states plays major role, initiates ultrafast internal conversion and contributes to the spectral broadening. Theoretical findings are finally compared with the available experimental and theoretical data and discussed in connection with the recorded DIBs.