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Title: Linear Absorption Spectrum of a Quantum Two-Dimensional Rotator Calculated using a Rotationally Invariant System-Bath Hamiltonian
Authors: Iwamoto, Yuki
Tanimura, Yoshitaka
Author's alias: 岩元, 佑樹
谷村, 吉隆
Issue Date: 28-Aug-2018
Publisher: AIP Publishing
Journal title: The Journal of Chemical Physics
Volume: 149
Issue: 8
Thesis number: 084110
Abstract: We consider a two-dimensional rigid rotator system coupled to a two-dimensional heat bath. The Caldeira-Leggett (Brownian) model for the rotator and the spin-Boson model have been used to describe such systems, but they do not possess rotational symmetry, and they cannot describe the discretized rotational bands in absorption and emission spectra that have been found experimentally. Here, to address this problem, we introduce a rotationally invariant system-bath (RISB) model that is described by two sets of harmonic-oscillator baths independently coupled to the rigid rotator as sine and cosine functions of the rotator angle. Due to a difference in the energy discretization of the total Hamiltonian, the dynamics described by the RISB model differ significantly from those described by the rotational Caldeira-Legget model, while both models reduce to the Langevin equation for a rotator in the classical limit. To demonstrate this point, we compute the rotational absorption spectrum defined by the linear response function of a rotator dipole. For this purpose, we derive a quantum master equation for the RISB model in the high-temperature Markovian case. We find that the spectral profiles of the calculated signals exhibit a transition from quantized rotational bands to a single peak after spectrum collapse. This is a significant finding because previous approaches cannot describe such phenomena in a unified manner.
Rights: The following article appeared in J. Chem. Phys. 149, 084110 (2018) and may be found at https://doi.org/10.1063/1.5044585.
The full-text file will be made open to the public on 28 August 2019 in accordance with publisher's 'Terms and Conditions for Self-Archiving'.
URI: http://hdl.handle.net/2433/241684
DOI(Published Version): 10.1063/1.5044585
PubMed ID: 30193481
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