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ABSTRACT: We report on full-dimensional vibrational quantum dynamics of the highly excited ammonia isotopologue NHD(2) using a newly developed potential energy surface and the MCTDH program package. The calculations allow to realistically simulate an infrared laser induced stereomutation reaction at the pyramidal nitrogen atom in the femtosecond time domain. Our results allow for a thorough qualitative and quantitative understanding of infrared photoinduced stereomutation kinetics, the underlying quantum dynamics, and the reaction mechanisms. Comparison is made with a previous, reduced dimensionality study of the same reaction [R. Marquardt, M. Quack, I. Thanopulos, and D. Luckhaus, J. Chem. Phys. 118, 643 (2003)], and it is shown that slight variances of reduced spaces lead to significantly different kinetics. Because the quantum dynamics depends subtly on variances of reduced spaces, reduced dimensionality treatments are not reliable even for qualitative predictions of the stereomutation kinetics. The first direct comparison between the Multiconfigurational Time Dependent Hartree [M. H. Beck, A. Jäckle, G. A. Worth et al., Phys. Rep. 324, 1 (2000)] and Unimolecular Reactions Induced by Monochromatic Infrared Radiation [M. Quack and E. Sutcliffe, QCPE Bulletin 6, 98 (1986)] program packages on a specific, four dimensional quantum dynamical problem allows for their full validation in the present work.
The Journal of chemical physics 11/2010; 133(17):174302. · 3.09 Impact Factor
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ABSTRACT: The present paper is devoted to a full quantum mechanical study of the cis-->trans isomerization of HONO. In contrast to our previous study [Richter et al., J. Chem. Phys. 120, 6072 (2004)], the dynamics is now performed in the presence of an external time-dependent field in order to be closer to experimental conditions. A six-dimensional dipole surface is computed. Using a previously developed potential energy surface [Richter et al., J. Chem. Phys. 120, 1306 (2004)], all eigenstates up to 4000 cm(-1) are calculated. We simulate the dynamics during and after excitation by an electromagnetic pulse whose parameters are chosen to efficiently trigger the isomerization. Our investigations show that there is a selective isomerization pathway.
The Journal of Chemical Physics 10/2007; 127(16):164315. · 3.33 Impact Factor
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ABSTRACT: We discuss the quantum dynamics of the excitation of a diatomic molecule in the presence of external force fields and the general role of orientation on the manipulation of molecular structure. We review the dynamics of the HF molecule in the presence of a static electric field during and after coherent infrared radiation. The time-dependent dynamics is induced by infrared multiphoton excitation and the time evolution of the rovibrational wave packet is calculated in configuration space. The coherent motion of rotational wave packets obtained from orientation in a static field is compared with the motion of rotational coherent states. Values are given for static field strengths needed to orient molecules such that their internal dynamics can be described by simplified, purely vibrational models. The results are discussed in comparison with the orientation of adsorbed molecules on metal surfaces. © 2004 Wiley Periodicals, Inc. Int J Quantum Chem, 2004
International Journal of Quantum Chemistry 02/2004; 99(4):439 - 451. · 1.36 Impact Factor
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ABSTRACT: The quantum dynamics of the HF molecule is investigated in the presence of a static electric field and coherent infrared radiation. The time dependent dynamics is induced by infrared multiphoton excitation and the time evolution of the rovibrational wave packet is calculated in configuration space. Results are given for static field strengths needed to orient molecules such that their internal dynamics can be described by simplified, purely vibrational models. For highly oriented HF molecules, time intervals of approximate duration of 70 fs occur repeatedly during and after the excitation in which the reduced vibrational wave packet motion is nearly semiclassical (“semiclassical windows”). The occurrence of these time intervals can be made more regular after the excitation, if the pulse duration is chosen adequately. © 2002 American Institute of Physics.
The Journal of Chemical Physics 02/2002; 116(8):3300-3308. · 3.33 Impact Factor
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ABSTRACT: The time dependent quantum dynamics of molecular rotations and vibrations during coherent infrared multiphoton excitation are investigated by calculation of the time evolution of the wave packet in the rotational and vibrational configuration space. Results are presented for the rovibrational motion of HF using recent potential energy and dipole moment functions developed elsewhere by ab initio calculations. Several initial conditions are studied, from the single rovibrational ground state to a superposition of states with different J quantum numbers corresponding to highly oriented molecules. A careful examination of the rovibrational wave packet motion allows for a simple interpretation of the rotational motion and the effects of different initial conditions on the intramolecular kinetics. It is found that, depending on the degree of orientation, the HF molecule undergoes very fast deorientation, faster than its “classical” rotational period, thus perturbing the generation of a semiclassical vibrational motion during the excitation process. © 2001 American Institute of Physics.
The Journal of Chemical Physics 01/2001; 114(2):826-835. · 3.33 Impact Factor
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ABSTRACT: In the context of studies of the intramolecular vibrational-energy redistribution (IVR) in molecules with the aid of the multiconfiguration time-dependent Hartree (MCTDH) method, we simulate the dynamics of the selective population of vibrational levels in H2CS in the presence of an external time-dependent field. The molecule is described by means of six valence polyspherical coordinates. The potential-energy surface (PES), the dipole moment function, and the kinetic energy are of direct-product form in these coordinates and hence perfectly adapted to MCTDH. In order to obtain the eigenstates and the corresponding transition moments of the system, recent developments of the MCTDH improved relaxation method, for which a first comprehensive description is given here, are exploited.
Chemical Physics.
