Issue 1, 2003

Dissipative wave packet dynamics of the intramolecular hydrogen bond in o-phthalic acid monomethylester

Abstract

We investigate the infrared laser-driven ultrafast dynamics of the carboxy-deuterated title compound in the condensed phase using a system–bath approach. The three-dimensional relevant system comprises the OD stretching and bending motion as well as a low-frequency out-of-plane twisting vibration modulating the hydrogen-bond strength. The dominant relaxation and dephasing channels are identified giving rise to three terms which contribute to the system–bath interaction: (i) A linear system-solvent coupling leading to the relaxation of the low-frequency mode. Here, a classical molecular dynamics simulation is performed to obtain the spectral density and thus the relevant relaxation time scale for this mode. (ii) A coupling which is quadratic in the system coordinates and responsible for pure dephasing. (iii) A fourth-order coupling which involves the release of vibrational energy into the environment by means of the simultaneous excitation of two intramolecular bath vibrations and a solvent mode. Using a quantum master equation approach it is demonstrated that this model is in accord with the results of recent infrared pump-probe and four-wave mixing experiments. The dynamics is discussed in terms of a diabatic representation defined with respect to the high-frequency stretching and bending modes. The behaviour of the low-frequency mode can be characterized as a dissipative wave packet motion in the diabatic ground state which contains contributions from bath-induced coherence transfer out of the initially excited diabatic state.

Article information

Article type
Paper
Submitted
02 Oct 2002
Accepted
01 Nov 2002
First published
18 Nov 2002

Phys. Chem. Chem. Phys., 2003,5, 79-86

Dissipative wave packet dynamics of the intramolecular hydrogen bond in o-phthalic acid monomethylester

O. Kühn and H. Naundorf, Phys. Chem. Chem. Phys., 2003, 5, 79 DOI: 10.1039/B209587D

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