Imaging Photodissociation Dynamics of Excited SiO Molecules at 193 nm with Laser Ablation Supersonic Beam^†

SiO is a wide-spread molecule found in interstellar space. Previous research has primarily focused on its spectroscopy, while its photodissociation dynamics is elusive to study due to high dissociation energy. Using time-sliced ion velocity imaging technique, we observed the Si(³P)+O(³P) photodissociation process resulting from the excitation of highly vibrationally excited SiO(X¹Σ⁺, v=13–18) molecules to the SiO(A¹Π, E¹Σ⁺) states at 193 nm. The vibrationally excited SiO molecules were generated via laser ablation of silicon rod with the collision of the oxygen molecular beam acting as carrier gas and reaction gas. The bond dissociation energy D_e(Si−O) is determined to be 67253 ± 110 cm⁻¹ (8.34 ± 0.01 eV) based on the kinetic energy distribution spectrum. The SiO photodissociation study has deepened our understanding of the mechanisms of silicon chemistry for silica-rich rocky meteors as they burn in the Earth’s atmosphere, and the dissociation of SiO from ablation of meteoroids following ultraviolet photon absorption.