Photodissociation of phosgene : Theoretical evidence for the ultrafast and synchronous concerted three-body process

• The potential energy surfaces for Cl2CO dissociation into CO+Cl+Cl in the lowest two electronic singlet states (S-0 and S-1) have been determined by the complete active space self-consistent field, coupled-cluster method with single and double excitations (CCSD), and equation-of-motion CCSD calculations, which are followed by direct ab initio molecular dynamics simulations to explore its photodissociation dynamics at 230 nm. It is found that the C-O stretching mode is initially excited upon irradiation and the excess internal energies are transferred to the C-Cl symmetric stretching mode within 200 fs. On average, the first and the second C-Cl bonds break completely within subsequent 60 and 100 fs, respectively. Electronic structure and dynamics calculations have thus provided a strong evidence that the photoinitiated dissociation of Cl2CO at 230 nm or shorter wavelengths is an ultrafast, adiabatic, and concerted three-body process. Since the two C-Cl bonds begin to break at the same time and the time interval between the two C-Cl bond broken fully is very short (similar to 40 fs), the photoinitiated dissociation of Cl2CO to CO+2Cl can be considered as the synchronous concerted process.

Nyckelord

3 body decay

initio molecular-dynamics

excited-state topology

sym-triazine

glyoxal photodissociation

dissociation

nm

chloride

photolysis

ethylene

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