Full-dimensional quantum dynamics of vibrationally highly excited NHD2

Full-dimensional quantum mechanical computations are carried out to investigate the photodissociation dynamics of Ã state NH(3) and ND(3) using the multiconfiguration time-dependent Hartree (MCTDH) method with recently developed coupled ab initio potential energy surfaces (PESs) [Z. H. Li, R. Valero, and D. G. Truhlar, Theor. Chim. Acc. 118, 9 (2007)]. To use the MCTDH method efficiently the PESs are represented as based on the high-dimensional model representation. The Ã ← X̃ absorption spectra for both isotopomers were calculated for the zeroth vibrational state of the ground electronic state. With a view to treating larger systems, Jacobi coordinates are used. Computations on the coupled PES are carried out for two-, three-, five-, and six-dimensional model systems to understand the validity of reduced-dimensional calculations. In addition to the fully coupled calculations, the effect of nonadiabatic coupling on absorption spectra is shown by propagating the initial wavepacket only in the Ã electronic state. The calculated absorption spectra are shown to be in good agreement with available theoretical and experimental observations. Comparisons with calculations using Radau and valence coordinates show the effect of including the symmetry of the system explicitly. Finally, branching ratios for loss of a hydrogen atom via the two available channels are calculated. These predict that the nonadiabatic product increases with the dimension of the calculations and confirm the importance of the full-dimensional calculations.

Section: Discussionsupporting

confidence: 80%

Section: B System Hamiltonianmentioning

confidence: 99%

A full-dimensional coupled-surface study of the photodissociation dynamics of ammonia using the multiconfiguration time-dependent Hartree method

Giri

Chapman

Sanz-Sanz

et al. 2011

“…We have, for instance, studied the cis-trans isomerization [5][6][7] of HONO or the inversion 8 of NHD 2 in full dimensionality.…”

Section: Introductionmentioning

confidence: 99%

Quantum dynamics study of fulvene double bond photoisomerization: The role of intramolecular vibrational energy redistribution and excitation energy

Blancafort

Gatti

Meyer

2011

Self Cite

The double bond photoisomerization of fulvene has been studied with quantum dynamics calculations using the multi-configuration time-dependent Hartree method. Fulvene is a test case to develop optical control strategies based on the knowledge of the excited state decay mechanism. The decay takes place on a time scale of several hundred femtoseconds, and the potential energy surface is centered around a conical intersection seam between the ground and excited state. The competition between unreactive decay and photoisomerization depends on the region of the seam accessed during the decay. The dynamics are carried out on a four-dimensional model surface, parametrized from complete active space self-consistent field calculations, that captures the main features of the seam (energy and locus of the seam and associated branching space vectors). Wave packet propagations initiated by single laser pulses of 5-25 fs duration and 1.85-4 eV excitation energy show the principal characteristics of the first 150 fs of the photodynamics. Initially, the excitation energy is transferred to a bond stretching mode that leads the wave packet to the seam, inducing the regeneration of the reactant. The photoisomerization starts after the vibrational energy has flowed from the bond stretching to the torsional mode. In our propagations, intramolecular energy redistribution (IVR) is accelerated for higher excess energies along the bond stretch mode. Thus, the competition between unreactive decay and isomerization depends on the rate of IVR between the bond stretch and torsion coordinates, which in turn depends on the excitation energy. These results set the ground for the development of future optical control strategies.

“…As in Ref. 27, the vibrational motion of the nuclei is parameterized by polyspherical Radau coordinates. The polyspherical approach 28, 29 is a powerful method for the derivation of the kinetic energy operator of molecular systems in curvilinear coordinates.…”

Section: Hamiltonian and Coordinatesmentioning

confidence: 99%

“…As a simplification, we consider the kinetic energy operator of the fundamental rotational state J = 0. 27 We assume throughout the paper that the molecule is ideally aligned along given axes (three-dimensional alignment) and that Hamiltonian (9) describes this aligned molecule. In Ref.…”

Section: Hamiltonian and Coordinatesmentioning

confidence: 99%

Laser-induced enhancement of tunneling in NHD2

Sala¹,

Guérin²,

Gatti³

et al. 2012

Self Cite

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 circularly polarized field improves the rotationally averaged tunneling probability at the end of the pulse.