0000000000140844
AUTHOR
Matthieu Sala
Laser control of the radiationless decay in pyrazine using the dynamic Stark effect
The laser control of the radiationless decay between the B(3u)(nπ*) and B(2u)(ππ*) states of pyrazine using the dynamic Stark effect has been investigated. A vibronic coupling model Hamiltonian in diabatic representation, including potential energy, transition dipole, and static polarizability surfaces as a function of the four most important vibrational modes of the molecule has been parametrized using multi-reference electronic structure calculations. The interaction of the molecule with a strong non-resonant laser pulse has been analyzed in terms of dressed potential energy surfaces. Because of the large polarizability difference between the vibronically coupled B(3u)(nπ*) and B(2u)(ππ*)…
The role of the low-lying dark np* states in the photophysics of pyrazine: a quantum dynamics study
The excited state dynamics of pyrazine has attracted considerable attention in the last three decades. It has long been recognized that after UV excitation, the dynamics of the molecule is impacted by strong non-adiabatic effects due to the existence of a conical intersection between the B2u(ππ*) and B3u(nπ*) electronic states. However, a recent study based on trajectory surface hopping dynamics simulations suggested the participation of the Au(nπ*) and B2g(nπ*) low-lying dark electronic states in the ultrafast radiationless decay of the molecule after excitation to the B2u(ππ*) state. The purpose of this work was to pursue the investigation of the role of the Au(nπ*) and B2g(nπ*) states in…
Full-dimensional control of the radiationless decay in pyrazine using the dynamic Stark effect
We present a full quantum-mechanical study of the laser control of the radiationless decay between the B3u(nπ(*)) and B2u(ππ(*)) states of pyrazine using the dynamic Stark effect. In contrast to our previous study [Sala et al., J. Chem. Phys. 140, 194309 (2014)], where a four-dimensional model was used, all the 24 degrees of freedom are now included in order to test the robustness of the strategy of control. Using a vibronic coupling Hamiltonian model in a diabatic representation, the multi-layer version of the multi-configuration time-dependent Hartree method is exploited to propagate the corresponding wave packets. We still observe a trapping of the wavepacket on the B2u(ππ(*)) potential …
Exploration of the Potential Energy Landscape of Aniline Using CASSCF and XMCQDPT2 Electronic Structure Calculations
In this chapter, the tools introduced in Chap. 2 are applied to the study of the photochemistry of aniline. This work has been initiated during a six-month fellowship in the group of Professor Helen Fielding in the Chemistry Department of University College London, in the framework of the FASTQUAST Initial Training Network.
Laser Driven Tunneling Dynamics in NHD $$_2$$ 2
This chapter is partly based on results and discussions published in Refs. M. Sala et al. J. Chem. Phys. 136, 194308 (2012) [1], M. Sala et al. J. Chem. Phys. 141, 164326 (2014) [2]. This material is reproduced with permission. Copyright [2012, 2014] AIP Publishing LLC.
Coherent destruction of tunneling in a six-dimensional model of NHD2: a computational study using the multi-configuration time-dependent Hartree method.
We investigate the phenomenon of coherent destruction of tunneling in a six-dimensional model of the NHD2 molecule. Two regimes are considered for the frequency of the laser field. A non-resonant regime where the frequency of the laser field is high with respect to the ground vibrational state tunneling splitting but smaller than the transition frequencies between the ground and excited vibrational states; and a quasi-resonant regime where the frequency of the laser field is close to the transition frequency between the ground and first excited vibrational states. In each case, we study the laser driven dynamics in the framework of the Floquet formalism and derive simple analytical formulas…
The Role of the Low-Lying $$n\pi ^*$$ n π ∗ States on the Photophysics of Pyrazine
In this chapter, the theoretical tools introduced in Chaps. 2 and 4 are applied to the study of the non-adiabatic relaxation dynamics of pyrazine after ultraviolet (UV) excitation.
Quantum dynamics of the photostability of pyrazine
We investigate the radiationless decay of photoexcited pyrazine to its ground electronic state using multireference electronic structure and quantum dynamics calculations. We construct a quadratic vibronic coupling Hamiltonian, including the four lowest electronic states and ten vibrational modes, by fitting to more than 5000 ab initio points. We then use this model to simulate the non-adiabatic excited state dynamics of the molecule using the multi-configuration time-dependent Hartree method. On the basis of these calculations, we propose a new mechanism for this decay process involving a conical intersection between the Au(nπ*) state and the ground state. After excitation to the B2u(ππ*) …
Laser-induced enhancement of tunneling in NHD2
We apply and explore techniques aiming at enhancing the tunneling by laser fields, originally developed for a one-dimensional model, to a complete six-dimensional vibrational model of the inversion motion in NHD(2). The computational study is performed with the multi-configuration time-dependent Hartree method. Assuming an ideal three-dimensional alignment we obtain a driven tunneling time twenty times smaller than the natural one, in rather good agreement with an oversimplified three-state model. In the case of one-dimensional alignment, a linearly polarized field leads to a poor enhancement of the tunneling probability, after averaging over the rotation about the alignment axis, whereas a…
Theory of Nuclear Quantum Dynamics Simulations
In Chap. 2, we have seen that the theoretical study of a molecular system is, in a vast majority of cases, separated in two steps. In a first step, the electronic structure of the system is studied by solving the electronic Schrodinger equation with fixed nuclei. This approach, combined with geometry optimization techniques, allows one to locate the important features of the various potential energy surfaces (PESs) of the electronic states of interest. In the context of photochemistry, as seen in Chap. 3, this approach allows one to characterize the various decay pathways of the molecule after photoexcitation. This information can then be used to interpret the various decay time constants o…
Basic Concepts and Methodology
In this chapter, the main concepts relevant for the theoretical study of elementary photochemical processes are briefly reviewed. The notions of vibronic coupling and conical intersection are first introduced. The main basic tools from the molecular electronic structure theory and their use for the exploration of potential energy surfaces are then presented.
Theoretical Tools for the Description of Strong Field Laser-Molecule Interaction
In this chapter, the main theoretical tools used in the work presented in the next two chapters on the laser control of the radiationless decay in pyrazine and of the tunneling dynamics in NHD\(_2\), are introduced.