Theoretical studies of atmospheric molecular complexes interacting with NIR to UV light

Abstract

The interaction of weakly bonded complexes of atmospheric constituents with the electromagnetic spectrum available in Earth’s atmosphere can induce direct excitation to electronic excited states as well as the excitation of higher vibrational states (overtones) of the electronic ground state. A better understanding of these phenomena requires improved theoretical support by including the anharmonic and vibro-electronic effects on both the band positions and transition intensities. In this work, generalized second-order vibrational perturbation and time-independent Franck–Condon and Herzberg–Teller computations are exploited together with a density functional theory (DFT)/coupled cluster (CC) scheme and its extension to the excited electronic states. Structural and spectroscopic properties are calculated for isolated formaldehyde and its complexes with H₂O, CO, SO₂ and H₂O₂, focusing on how small molecules may affect the interactions with NIR to UV irradiation.