arXiv subjects

Sebastian Mai

Publications and source records attributed to Sebastian Mai.

23 records · Page 2Linked to original sources

arXiv2016

The DNA Nucleobase Thymine in Motion - Intersystem Crossing Simulated with Surface Hopping

We report ab initio excited-state dynamics simulations on isolated thymine to investigate the mechanism of intersystem crossing, based on CASSCF potential energy surfaces and the \textsc{Sharc} surface hopping method. We show that even though $S_2 \rightarrow S_1$ internal conversion is not described accurately with CASSCF, intersystem crossing can be correctly simulated. Intersystem crossing in thymine occurs from the $S_1$ ($^1nπ^*$) minimum, via a nearby crossing with $T_2$ ($^3ππ^*$). The system further relaxes via ultrafast internal conversion in the triplet manifold to the $T_1$ ($^3ππ^*$) state. The simulations reveal that, once the system is trapped in the $^1nπ^*$ minimum, intersystem crossing might proceed with a time constant of 1~ps. Furthermore, the change of the system's electronic state is accompanied respectively by elongation/shortening of specific bonds, which could thus be used as indicators to identify which state is populated in the dynamics.

physics.chem-ph↗

arXiv2016

Direct Observation of Molecular Oxygen Production from Carbon Dioxide

Oxygen ($O_2$) is one of the most important elements required to sustain life. The concentration of $O_2$ on Earth has been accumulated over millions of years and has a direct connection with that of $CO_2$. Further, $CO_2$ plays an important role in many other planetary atmospheres. Therefore, molecular reactions involving $CO_2$ are critical for studying the atmospheres of such planets. Existing studies on the dissociation of $CO_2$ are exclusively focused on the C--O bond breakage. Here we report first experiments on the direct observation of molecular Oxygen formation from $CO_2$ in strong laser fields with a reaction microscope. Our accompanying simulations suggest that $CO_2$ molecules may undergo bending motion during and after strong-field ionization which supports the molecular Oxygen formation process. The observation of the molecular Oxygen formation from $CO_2$ may trigger further experimental and theoretical studies on such processes with laser pulses, and provide hints in studies of the $O_2$ and $CO_2^+$ abundance in $CO_2$-dominated planetary atmospheres.

physics.chem-ph↗

arXiv2015

Photoelectron Spectra of 2-Thiouracil, 4-Thiouracil and 2,4-Dithiouracil

Ground- and excited-state UV photoelectron spectra of thiouracils (2-thiouracil, 4-thiouracil and 2,4-dithiouracil) have been simulated using multireference configuration interaction calculations and Dyson norms as measure for the photoionization intensity. Except for a constant shift, the calculated spectrum of 2-thiouracil agrees very well with experiment, while no experimental spectra are available for the two other compounds. For all three molecules, the photoelectron spectra show distinct bands due to ionization of the sulphur and oxygen lone pairs and the pyrimidine $π$ system. The excited-state photoelectron spectra of 2-thiouracil show bands at much lower energies than in the ground state spectrum, allowing to monitor the excited-state population in time-resolved UV photoelectron spectroscopy (TRPES) experiments. However, the results also reveal that single-photon ionization probe schemes alone will not allow monitoring all photodynamic processes existing in 2-thiouracil. Especially, due to overlapping bands of singlet and triplet states the clear observation of intersystem crossing will be hampered.

physics.chem-ph↗

arXiv2014

Excited-State Dynamics in SO2: II. The Role of Triplet States in the Bound State Relaxation Studied by Surface-Hopping Simulations

The importance of triplet states in the photorelaxation dynamics of SO2 is studied by mixed quantum-classical dynamics simulations. Using the Surface Hopping including ARbitrary Couplings (Sharc) method, intersystem crossing processes caused by spin-orbit coupling are found occuring on an ultrafast time scale (few 100 fs) and thus competing with internal conversion. While in the singlet-only dynamics only oscillatory population transfer between the 1B1 and 1A2 states is observed, in the dynamics including singlet and triplet states we find additionally continuous ISC to the 3B2 state and to a smaller extent to the 3B1/3A2 coupled states. The populations obtained from the dynamics are discussed with respect to the overall nuclear motion and in the light of recent TRPEPICO studies [Wilkinson et al., paper I].

physics.chem-ph↗

arXiv2013

Stationary Josephson effect in a short multi-terminal junction

We study the dc Josephson effect and the density of states in a multiterminal structure of cross-type geometry which consists of four superconducting electrodes connected by one-dimensional normal or ferromagnetic wires. We find that the Josephson current $I_{Jz}$ has a sinusoidal dependence on the phase difference $ϕ_z$ between the superconductors in the horizontal wire with a critical current $I_c$ that can be varied by changing the phase difference $ϕ_y$ between the superconductors in the vertical wire. The period of the function $I_{Jz}(ϕ_z)$ depends on the ratio of the interface resistances $R_{Sn,z}/R_{Sn,y}$ being equal to $2π$ if this ratio is small and equal to $4π$ in the opposite limit. We also calculate the amplitudes of both the singlet and the odd-frequency triplet component in the system under consideration. The triplet component amplitude may be significantly larger than the amplitude of the singlet component.

cond-mat.supr-con↗