An ab initio quantum dynamics simulation of UV absorption spectrum of methyl vinyl ketone oxide

Abstract

The spectroscopy of the four-carbon Criegee intermediate, methyl vinyl ketone oxide (MVK-oxide), following UV excitation to the B state (corresponding to the first $\pi^* \leftarrow \pi$ electronic transition) is studied theoretically, relied on single reference electronic wave function and a quantum dynamical approach for the nuclear motion. Two interacting electronic states $B{}^1\rm{A'}$ and $C{}^1\rm{A'}$ together with two nuclear degrees of freedom (\ce{O-O} stretching and \ce{C-O-O} bending modes) are considered in the dynamical approach. The computed absorption spectrum is found to agree well with the available experimental recordings. The existence of the weak oscillatory structures in the absorption spectrum are argued likely due to the fact that the excitation energy range of the first $\pi^* \leftarrow \pi$ electronic transition is below the energy barrier of the diabatic B state ($\sim 215$~nm) and thus below the sufficiently deep well occurring at the intermediate \ce{O-O} distances. Thissuggests the recurrences of the wavepacket, which might be considered as origin of the weak oscillatory structures in the absorption spectrum. The computed electronic excitation profile of MVK-oxide is predicted to peak at $373$ nm.

UV Absorption Spectroscopy of the Conformer-Dependent Reactivity of the Four Carbon Criegee Intermediate of Methyl Vinyl Ketone Oxide: An Ab initio Quantum Dynamics Study

“…The potential energy surfaces (PESs) were computed using the EOM-CCSD method. Even though a good agreement was achieved between the computed spectrum and experimental spectra reported by Caravan et al and Vansco et al achieved, ,, the computed spectrum (modeled by the PESs computed by the EOM-CCSD method) still is not capable of producing the recently measured spectrum by Lin et al in the wavelength range of 360–480 nm . This is more likely due to employing an inadequate electronic structure method (EOM-CCSD) for computing PESs, often yielding poor predictions of the absorption spectrum.…”

“…The model Hamiltonian used in the current work is a modified version of the one employed in our previous work . This modification is related to the improvement in the quality of the PESs of the excited states along the relevant vibrational modes.…”

“…The kinetic operator of T N is computed by using the G-matrix method technique (described in more detail in refs and ), where atoms C and O play roles in the evaluation of the G-matrix elements and the kinetic operator. Thus, the kinetic operator is In eq , the variables R and θ refer to the O–O stretch and C–O–O bend coordinates. The coefficients used in eq are defined in the following where m O = 15.999 and m C = 12.011 in atomic mass units.…”

“…The EOM-CCSD method used for computing PESs of the relevant excited states in ref is not a trustworthy method to compute the energies at the asymptote region of the O–O stretching mode due to the fact that the EOM-CCSD method does not produce converged energies in this region. Thus, the photodissociation dynamics of MVK-oxide need to be reinvestigated based on accurately computed PESs of the excited states using, e.g., a multireference electronic structure method.…”

Master Equation Studies of the Unimolecular Decay of Thermalized Methacrolein Oxide: The Impact of Atmospheric Conditions

“…Among the important kinetic pathways followed by Criegee intermediates under thermal conditions are: conformational dynamics (involving rotation about one or more carbon–carbon or carbon–oxygen bond within the molecule), hydrogen transfer reactions (which can lead to the formation of OH radicals via hydroperoxide formation), ring-closing reactions (leading to the formation of dioxirane structures), and alternative ring-closing mechanisms (leading to formation of dioxole structures). , Many of the dioxole and dioxirane structures are believed to undergo further unimolecular decay. With respect to the ozonolysis of isoprene, the majority of the experimental and theoretical studies have focused on the properties and reactivity of MVK ,− ,− and formaldehyde oxides, ,− with MACR oxide being relatively less studied. ,− ,− At the same time, it is clear that MACR oxide can play an important role in the ozone-derived chemistry of isoprene: as described by others, and discussed below, anti-MACR oxide is unusually long-lived (τ ≈ 0.10 s at 298 K) with respect to unimolecular decay, ,, making this Criegee intermediate a potentially potent contributor to bimolecular chemistry in the atmosphere.…”