Theoretical Analysis of the Formylmethylene Anion Photoelectron Spectrum: Importance of Wolff Rearrangement Dynamics.

Photoelectron spectroscopy of a molecular anion is very useful for investigating the transition state and intermediate regions on the reactive potential energy surfaces of a neutral system. In this work, we theoretically analyzed the previously measured photoelectron spectrum of the formylmethylene anion, HCCHO-. We simulated the photoelectron spectra for both the singlet and triplet states using the semiclassical method with quantum nuclear densities and Franck-Condon factor calculations with harmonic vibrational analysis. We also performed real-time quantum dynamics calculations to elucidate the importance of the Wolff rearrangement process, which leads to the stable product ketene from the carbene intermediate on the neutral singlet potential energy surface.

Spin-inversion mechanisms in O2 binding to a model heme compound: A perspective from nonadiabatic wave packet calculations.

Spin-inversion dynamics in O2 binding to a model heme complex, which consisted of Fe(II)-porphyrin and imidazole, were studied using nonadiabatic wave packet dynamics calculations. We considered three active nuclear degrees of freedom in the dynamics, including the motions along the Fe-O distance, Fe-O-O angle, and Fe out-of-plane distance. Spin-free potential energy surfaces for the singlet, triplet, quintet, and septet states were developed using density functional theory calculations, and spin-orbit coupling elements were obtained from CASSCF-level electronic structure calculations. The spin-inversion mainly occurred between the singlet state and one of the triplet states due to large spin-orbit couplings and the contributions of other states were extremely small. The present quantum dynamics calculations suggested that the narrow crossing region model plays a dominant role in the O2 binding dynamics. In addition, the one-dimensional Landau-Zener model underestimated the nonadiabatic transition probability.

Reduced-Dimensionality Quantum Dynamics Study of the 3Fe(CO)4 + H2 1FeH2(CO)4 Spin-inversion Reaction.

Many chemical reactions of transition metal compounds involve a change in spin state via spin inversion, which is induced by relativistic spin-orbit coupling. In this work, we theoretically study the efficiency of a typical spin-inversion reaction, 3Fe(CO)4 + H2 1FeH2(CO)4. Structural and vibrational information on the spin-inversion point, obtained through the spin-coupled Hamiltonian approach, is used to construct three degree-of-freedom potential energy surfaces and to obtain singlet-triplet spin-orbit couplings. Using the developed spin-diabatic potential energy surfaces in reduced dimensions, we perform quantum nonadiabatic transition state wave packet calculations to obtain the cumulative reaction probability. The calculated cumulative reaction probability is found to be significantly larger than that estimated from the one-dimensional surface-hopping probability. This indicates the importance of both multidimensional and nuclear quantum effects in spin inversion for polyatomic chemical reaction systems.

Spin-inversion mechanisms in O2 binding to a model heme complex revisited by density function theory calculations.

Spin-inversion mechanisms in O2 binding to a model heme complex, consisting of Fe(II)-porphyrin and imidazole, were investigated using density-functional theory calculations. First, we applied the recently proposed mixed-spin Hamiltonian method to locate spin-inversion structures between different total spin multiplicities. Nine spin-inversion structures were successfully optimized for the singlet-triplet, singlet-quintet, triplet-quintet, and quintet-septet spin-inversion processes. We found that the singlet-triplet spin-inversion points are located around the potential energy surface region at short Fe-O distances, whereas the singlet-quintet and quintet-septet spin-inversion points are located at longer Fe-O distances. This suggests that both narrow and broad crossing models play roles in O2 binding to the Fe-porphyrin complex. To further understand spin-inversion mechanisms, we performed on-the-fly Born-Oppenheimer molecular dynamics calculations. The reaction coordinates, which are correlated to the spin-inversion dynamics between different spin multiplicities, are also discussed.

Theoretical Study on the Spectroscopic Observation of Intersystem Crossing between 3B1 and 1A1 States of GeH2 Using the GeH2- (2B1) Anion.

We performed nonadiabatic quantum wave packet dynamics calculations to simulate the photodetachment spectrum of the GeH2- (2B1) anion. We developed the (4 × 4) diabatic potential energy surfaces to describe the intersystem crossing transitions between the neutral 1A1 and 3B1 states induced by spin-orbit interactions based on ab initio calculations. The spin-orbit coupling matrix elements were calculated using the Breit-Pauli Hamiltonian with the spin-free states obtained from the multireference configuration interaction method. The calculated photodetachment spectrum showed many intense peaks that could be assigned to the vibrational states mostly associated with the pure singlet or triplet spin states. However, we also found weak satellite peaks that could be assigned to vibrational states consisting of the highly excited vibrational state on the singlet surface and the low-lying vibrational state on the triplet surface.