New mechanism for non-trivial intra-molecular vibrational dynamics |
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Authors: | V A Benderskii and E I Kats |
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Institution: | (1) Institute of Chemical Physics Problems, 142432 Chernogolovka, Russia;(2) Laue-Langevin Institute, 38042 Grenoble Cedex 09, France;(3) L.D. Landau Institute for Theoretical Physics, RAS, Moscow, Russia |
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Abstract: | We investigate the time evolution process of one selected (initially prepared by optical pumping) vibrational molecular state
S, coupled to all other intra-molecular vibrational states R of the same molecule, and also to its environment Q. Molecular
states forming the first reservoir R are characterized by a discrete dense spectrum, whereas the environment reservoir Q states
form a continuous spectrum. Assuming the equidistant reservoir R states we find the exact analytical solution of the quantum
dynamic equations. S-Q and R-Q couplings yield to spontaneous decay of the S and R states, whereas S-R exchange leads to recurrence
cycles and Loschmidt echo at frequencies of S-R transitions and double resonances at the interlevel reservoir R transitions.
Due to these couplings the system S time evolution is not reduced to a simple exponential relaxation. We predict various regimes
of the system S dynamics, ranging from exponential decay to irregular damped oscillations. Namely, we show that there are
possible four dynamic regimes of the evolution: (i) independent of the environment Q exponential decay suppressing backward
R - S transitions, (ii) Loschmidt echo regime, (iii) incoherent dynamics with multicomponent Loschmidt echo, when the system
state is exchanged its energy with many states of the reservoir, (iv) cycle mixing regime, when long time system dynamics
looks as a random-like. We suggest applications of our results for interpretation of femtosecond vibration spectra of large
molecules and nano-systems. |
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Keywords: | PACS" target="_blank">PACS 05 45 -a Nonlinear dynamics and chaos 72 10 -d Theory of electronic transport scattering mechanisms |
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