Does chlorine peroxide absorb below 250 nm?

Area of Science:

• * Quantum Chemistry
• * Spectroscopy
• * Atmospheric Chemistry

Background:

• * Chlorine peroxide (ClOOCl) plays a role in stratospheric ozone depletion.
• * Understanding the electronic excited states of ClOOCl is crucial for atmospheric photochemistry.
• * Previous studies have focused on the singlet excited states, with limited information on triplet states.

Purpose of the Study:

• * To computationally investigate the low-lying singlet and triplet electronic excited states of ClOOCl.
• * To determine the excitation energies and oscillator strengths for these states.
• * To predict the spectral properties and potential dissociation pathways of ClOOCl.

Main Methods:

• * Employed excited state coupled cluster response (CC) methods.
• * Utilized the complete active space self-consistent field (CASSCF) method.
• * Incorporated the full Breit-Pauli spin-orbit (SO) operator for accurate spin-forbidden transitions.

Main Results:

• * Predicted a weakly absorbing triplet state lying below the lowest absorbing singlet excited state.
• * Calculated an absorption maximum for this triplet state at approximately 385 ± 25 nm.
• * Determined that the lowest triplet state is dissociative, leading to the formation of ClOO and Cl.

Conclusions:

• * The existence of a low-lying, weakly absorbing triplet state in ClOOCl has been computationally confirmed.
• * This triplet state's absorption profile suggests a potential role in atmospheric photolysis.
• * The calculated dissociation pathway provides insight into ClOOCl's reactivity in the atmosphere.