Page 25 - Book of Invited & Keynotes Talks

th
8 Biannual Conference on Chemistry - CHEM 08
The Nature of the Oxygen-Oxygen Bond in 1,2-Dioxetane.
Electronic Structure, QTAIM and Nonadabatic Dynamics

Study
Rifaat Hilal
Chemistry Department, Faculty of Science, Cairo University, Cairo, Egypt

ABSTRACT
The nature of the O-O bond in peroxides and 1,2-dioxetane in particular are
examined and discussed. The anisotropy in charge distributions and van der Waals
radii of atoms in such molecular systems are scrutinized. This provides an
understanding of their unusual molecular configuration, binding and recognition
modes involved in new types of molecular assembling and engineering. This work
would lead to the design of intriguing molecular systems exploiting anisotropic
noncovalent interactions. A number of single-reference post Hartree-Fock methods,
namely CIS, symmetry adopted cluster configuration interaction (SAC-CI),
equation of motion coupled cluster (EOM-CCSD) and time-dependent density
functional theory (TDDFT), were used to investigate the excited state properties and
photochemical dissociation of 1,2-dioxetane. Results are in good agreement with
experimental data. The decay of the excited states of 1,2-dioxetane in the gas phase
was examined by simulating the UV photoabsorption spectrum and nonadiabatic
dynamics at the TDDFT M06-2X level of theory. The spectrum, composed of 10
excited states, was simulated with the nuclear ensemble approximation, sampling a
Wigner distribution with 500 points. Dynamics simulations were done with the
surface hopping method, Photodynamic simulations of the excited states of 1,2-
dioxetane have been started in two different spectral windows, namely, 7.5 and &
9.0 eV, corresponding to populations of states S6 and S8, respectively. In each case,
we examined the dynamics in the first 100 fs time domain. Dynamics simulations
starting from these two energy windows show reaction pathways, leading to two
main products. The dynamics in the spectral window centered about 7.5 eV show
*
24% probability to originate from excited state 6 (nO-σ CO). Whereas, dynamics in
the spectral windows centered about 9.0 eV, show 67% probability to originate from
*
state 7 (nO-σ OO).
Key Words: peroxide bond, dioxetane, TDDFT calculation, excited states, surface
hopping

TalkDate: Tuesday 3 March 2020
Place:Hall A
Time: 3:55-4:35

BOOK OF INVITED SPEAKERS & KEYNOTES CHEM 08 (2020) Page 25